In the past couple of days, I've seen at least two threads where someone used "the line" simply because they disagreed with something a previous poster said.
There is a difference between an assumption and an opinion.
TAIA is one of the great comeback lines of all time, but it doesn't apply to all circumstances. Using it inappropriately reduces it to a quick, sitcom "zinger" and dilutes it's overall effect. This is especially true on a forum where there is time and space to politely clarify, debate, and express oneself.
Of course, this is just my humble.......opinion. 
CRUD MONKEYS! I couldn't agree with you more! I was thinking about starting a thread about this exact same thing as apparently others were too. Its being way overused and will soon become as meaningless as "whatever".
You might, you may = not an assumption only a statement of possibility
I think, IMHO = only your opinion, you are not stating it as a fact
Its possible = again not an assumption
According to your line of thinking = making an analogy to a previous statement, again not an assumption
Way to act = making a statement of your personal opinion, not an assumption
I will not = a statement of personal belief = not an assumption
You look fatter, you must be pregnant = you can use the line
Your husband flirts too much, he's going to cheat on you = you can use the line
Your child is retarded, his eyes look funny = you can use the line
Your wife is too loud, she's wasted = you can use the line
Your house is too small, no one will come to your parties = you can use the line
You're a nobody if you can't afford a cell phone = you can use the line
See the difference. Its only an assumption if its a statement presented as being factual. I don't think nosy questions qualify as assumptions because they are questions and not a statement. Nosy question askers need to have their shoes squeezed with a puzzled look and a "why do you want to know" asked in return. Pretend to not understand the question and make them squirm, they will probably stop.
You must be careful in accusing people of making assumptions and be certain that they are indeed assumption, not just something you don't like hearing. Many, many times I have read that line used here when it makes no sense at all.