Abbreviated way of saying you've already seen something. Short for "2 cool", originally "too cool for you", meaning you're too cool to be shown anything new.
Randy: OMG CHECK OUT THESE PICTURES OF CATS!
Jimtrod: 2c
An abbreviation of the phrase 'Second Choice' which can be used to describe a number of things, but mainly aimed an a boy/man who has been turned to after the first choice has been lost.