How to react to an awkward comment.

Comments can be constructive or senseless but worst is, people normally make senseless ones. Sometimes, they can just keep going on and on, and all I want to do is cut their tongue off. -.-

Anyway, here are some cases...

Case 1(definitely constructive xP):
Friend/Foe:
Wah, you look so pretty today lei!
Me:
No la! You're prettier.

Case 2 (senseless):
Friend/Foe:
Omg! This question so easy! You don't know how to do??
Me:
ok.. My ability to percieve is not as good as yours. Apparently, your grammar isn't that good either. *smiles* So, how do you do this question?

Come on.. Be humble, man! Learn from your mistakes.

Case 3 (TOTALLY SENSELESS):
Friend/Foe(thinks she/he's damn good):
Omg! How stupid can you be?? You look like an idiot! Your bag is so ugly! You're such an embarrassment!
Me:
>.> *stares* So? Why the **** do you even give a damn? It's my bag?!?! So, what do you want me to do to my bag? Throw away? Who gives you the right to even comment on my things? You're a renowned bag designer? -.- Stop making pointless comments which doesn't benefit anybody. (Actually, most of the time, I would choose to keep quiet or reply with a 'ok')

Why bother about douchebags who criticize people's intelligence when they don't even look at themselves in the first place. If you want to comment on someone's mistakes, you should kindly provide information exactly on what is the mistake and how to improve?

Just a bit off point, I wanna rant about CCAs being compulsory. GOSH! JC life can seriously make someone go bald (esp if you get into my JC. -.-) I regretted choosing this path, (wrong JC, wrong class, wrong friends). I SHOULD HAVE JUST GONE TO POLY! It's more suitable for me. :D