There are a lot of informal responses that essentially mean "I am not only rejecting the offer you just made, but I'm insulted that you made it."
Repeating other answers, "forget it" is a good phrase to use when you have previously rejected such offers in a friendlier way but the subsequent offers are not improving. The sense here is that the other party is clearly not trying hard enough to make a legitimate offer and you are frustrated to the point of giving up.
"Thanks, but no thanks" can be taken different ways; in your case you want to apply a sarcastic tone, making it clear that you really have no gratitude towards the other party. Slightly more assertive is "Thanks for nothing", which makes it explicit that you place no value on the offer being made.
A slightly less agressive option is "I'll pass", which has an implication that the initial offer was so unacceptable that you aren't even considering trying to improve it. There is less of an "angry" tone here as much as a "dismissive" one, but that can often get your point across as well.
Another reply suggested "don't insult my intelligence" which is good, since it indicates exactly why you are angry, but may not apply depending on what's being offered. (e.g. I wouldn't consider a low salary increase an insult to my intelligence as much as to the value of my work.) The more general form of "I'm insulted" gets the same point across.
All of these are very informal, and depending on the context would even be insulting back to the other party, since you are rejecting their offer with no indication why. In the example of a salary increase from your boss, (assuming for whatever reason that you chose to ignore social conventions of politeness) I would go with something more formal that specifically describes how the offer was deficient, such as "That's unacceptably low" or "That's not worth my time."