A word for showing a bit of anger that you are not satisfied with what is offered?

If you want to sound angry then you can say

Thanks for nothing.

This phrase is uttered when what someone has done for you has not produced satisfactory results, or has made your life worse. It can also be used in the situation where someone offers you something you don't want.

Verbally, I would say "forget it" to indicate that I don't want the offer and that I'm in a bit of a snit about it, with the right intonation, though.

For written communication, I cannot think of an idiomatic way of expressing a slight "bit" of anger. Anything you write could be (over)interpreted in a way that makes you sound like a boob...IMO it's best to explicitly state your reason for dissatisfaction, rather than depend on a phrase or idiom to express it.

An offer that you are resigning yourself to:

• That'll have to do
• A compromise
• Oh you shouldn't have ( more informal, requires a sarcastic or negative tone, else it can be used in more positive situations sometimes, varies from place to place culturally, also try Oh you shouldn't have, no, really, you shouldn't have bothered )

For an offer that is insufficient, is not good enough:

• Thanks but no thanks
• An unacceptable offer
• A laughable offer

If you really want to show anger/disdain:

• Are you taking the piss?
• Don't insult my intelligence

To convey that you scornfully decline to accept an offer...

spurn - to reject with disdain or contempt.

For example, "He spurned the offer", "She spurned his advances".