I hate when people type or write like this: diz (this) wat, dat, mii (my), & when people put double letters in a word for example thiis or when they add a "z" at the end of a word instead of an "s" it annoys me so much & makes them look dumb like they can't spell or something!!!! Lol
That bothers me as well, especially when it's done by grown ups,lol.
Around here the kids shorten words like saying "totes BFF" for total BFF and Obvi for obviously. It tends to get under my skin especially since I work at the high school and have to listen to it often.
Okay, this one is not just a teen thing, but is very prevalent online apparently: the phrase "I balled my eyes out". To the internet community at large, the correct spelling is "bawling", NOT "balling". I don't even know how someone would "ball" their eyes out, but every time I see this I envision golf balls and a trip to the ER! yuck!