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My mother just blew me off.

My mother just blew off bringing the car seat.

You done been blown off.

The verb phrase blow off can take an object immediately after blow (especially for pronouns or names) or after off (for noun phrases denoting tasks like work). According to the Oxford English Dictionary (in "blow, v.1") it means both disregarding someone else and shirking a job or duty:

transitive. to blow off:

(a) (now U.S. slang) to rebuff, to reject the advances of (a person); to ignore, disregard, dismiss;

(b) U.S. slang, to shirk or evade (a job or duty), to stay away from (school or work) without permission or good reason.

If you're British, you may have recourse to blow out, with similar valences:

4. transitive. Chiefly British.

To let (a person) down or shut (a person) out; to rebuff, reject the advances of (a person). Also: to fail to keep (an appointment), esp. deliberately, to jilt; to shirk. Cf. earlier to blow off at Additions.

Blow off especially pertains to your situation because your mother has both disregarded your concerns and has shirked the task at hand. Blow out might pertain more if she missed the appointment entirely, rather than neglecting some part of meeting you.

The problem is I don't think there's an English word for exactly this, because you said your mother thought you were being 'fussy' about this. It certainly was not such strong opposition to suggest 'flak' which would be far too strong.

Flak is like military shells (figuratively). Saying you were 'dissed' doesn't sound too 80sish to me, just not quite right. That's more like she put you down over it (not what happened). I think the closest you can get to it is something a lot milder, like 'she gave me a little heat about it'. But I wouldn’t say 'heat' alone, just 'a little heat'. It needs to be a word or phrase that suggests you were worrying unnecessarily about something, in her opinion.

Consider dismiss.

dismiss
2 Treat as unworthy of serious consideration.
‘When I campaigned for Police Community Support Officers in 2000, as the Mayoral candidate for London, the idea was dismissed by my opponents.’
- ODO

In the context of the examples you raise, dismiss tends to apply more naturally to the ideas rather than the people. Dismissing the person is a lot more offensive than dismissing the idea, though in the second example below, it could be read as a metonymic dismissal of the idea.

• When I reminded her about the car seat, she just dismissed [it / the idea].


• The parent who brought up the no-nut thing was dismissed by some of the others.

To dismiss an idea is to consider it so trivial that it doesn't bear further discussion. You can say that someone's attitude was dismissive, or even that they were dismissive. To complain that you were dismissed often implies that you were offended by the dismissal.

When using dismiss to mean the setting aside of something trivial, it's usually pretty clear that the one doing the dismissing considers the thing to be trivial. Whether it actually was or wasn't trivial relies on the context.

Guff[guhff]
noun Informal.

1) empty or foolish talk; nonsense.

2) insolent talk.

Source: Dictionary.com

———

Grief
noun

3) informal trouble or annoyance:

people were giving me grief for leaving ten minutes early

Source: Dictionary.com

———

The phrasing I would suggest would be:

When I reminded her about the car seat, she just gave me guff (grief).

The parent who brought up the no-nut thing was given grief (guff) by some of the others.

In my interpretation:

• guff implies the person doesn’t know what they are talking about.

• grief implies the person is affecting you.

Ignore, perhaps?

My mother just ignored me.

Or other phrases with similar meaning -

pay no attention

take no notice

brush aside (my) concerns

It's a bit like intimidation - you have a concern you think is legitimate, but they're trying to bully or browbeat you into submission.

Flout?
ARCHAIC
mock; scoff.
"the women pointed and flouted at her"

I quite like 'dismissed my concerns', though it doesn't roll off the tongue. I think 'diss' derives from 'disrespect'

Your examples seem to involve a two-step process.

First, someone denies a fact, cannot admit a mistake, downplays the gravity of a situation. --> The direct object of such verbs are inanimate, things, concepts. I call this aspect the DISMISSAL.

Second, this behavior then psychologically affects someone, disrespects a person, annoys their close ones. --> The direct object of such verbs are animate, people, humans. I call this aspect the PSYCHOLOGY.

There are generally no single verbs to express complex, two-step semantics of this kind, i.e. having an attitude towards a thing + affecting a person at the same time. You are therefore unlikely to find one specific verb to express exactly and only the kind of concept you're describing.

Verbs for the former step (depending on the form of the dismissal):

She belittled, trivialized, dismissed, ignored, brushed aside, downplayed, denied my concerns.

Verbs for the second step (depending on what the psychological effects are):

She disrespected, scoffed at, pooh-poohed, made fun of, disparaged, gaslighted, annoyed, insulted, bothered, exasperated, vexed, deprecated me.

The best solution to express the situation you're describing might be to be explicit and pick two verbs, one to explain what had happened, the other to expresses the psychological consequences.

For example:

(1) When I reminded her about the car seat, she just [_DISMISSALtrivialized my concerns], which [_PSYCHOLOGYpissed me off].

(2) When I reminded her about the car seat, she just [_PSYCHOLOGYannoyed me so much] with [_DISMISSALher inability to admit mistakes].

(3) The no-nut issue was [_DISMISSALjust completely dismissed] by some parents and [_PSYCHOLOGYthat's just so frustrating and indecent].

(4) The parent who brought up the no-nut thing was [_PSYCHOLOGYtotally disrespected] by some of the others when [_DISMISSALthey came up with these idiotic conspiracy theories].

This question is as much about inter-personal conflicts and anger-management as it is about English linguistics. So I'd go for an explicit expression that is a bit longer but really says what you want to say over a vague expression that may be shorter but could communicate ideas imprecisely or ineffectively.

An idiom which works quite well (especially in the first example sentence) is turn a deaf ear (to someone or something).

When I reminded her about the car seat, she just turned a deaf ear
to me.

The parent who brought up the no-nut thing was turned a deaf ear
to by some of the others.

TFD(idioms):

turn a deaf ear (to someone or something)

To ignore or refuse to listen to someone or something; to fail to pay attention to
something someone says.

The government has been turning a deaf ear to
the pleas of its most vulnerable citizens.

I'll never forgive myself
for turning a deaf ear when my roommate was clearly crying out for help.

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There seem to be at least two aspects to this:

Action and Reaction - on the parts of each of the two parties in the conversation.

The first party outlines the perceived problem.

The second party listens and disagrees.

The second party responds - either defensively or offensively.

If the response is defensive, the speaker's goal is to deflect negative attention and exonerate themselves from blame and the first party would be focused on the second party's behaviour.

In this case, the following would work:

Passing the buck

When I brought it up, she just bucked
me.

Synonyms include:

Duck [the issue], dodge [the issue]

Other options, depending on context, age, etc., include:

(S)He dimissed me.

(S)He went into this disgussion, which left me ...

(S)He totally squanched the issue

If the response is offensive, then the intention is to insult or cause psychological harm. In this case, the first party would be focused on their own state and the following could work:

Depending on the context, age, etc., if left speechless, they could say:

(S)He burned me. (Def. 5)

if affronted:

(S)He dissed [on] me. (Def. 5)

If there's a gender bias thing going on:

He became totally dicksmissive.

She became totally titsmissive.

If a person can't handle a particular task, they can be labeled unreliable.

If an unreliable person gets argumentative when challenged, you can describe them as quarrellous, stubborn, headstrong, or any associated synonym

Someone who will argue a losing position or who always has to be right could be pejoratively labeled a know-it-all.