Perfect Comeback to any insult. Or even sometimes, a conversation ender.

A sassy face to show that you give 0 fucks

-but you secretly give many fucks.

Short for "you". Used by people who are too lazy to make TWO FUCKIN' EXTRA KEYSTROKES. I imagine they all must look like that Jarred asshole, pre-Subway.

"In actuality what has been stated applies more directly to the former poster than to myself."

A parody of other emoticons.
Like people who abuse "LOL" "XD" and other emoticons/abbreviations, :u serves absolutely no purpose. In fact, it merely takes up space. Abuse it wisely.

A worthless shortening of a three letter word.

Pleased/smiling emoticon. Also seen without parenthesis.