SxE stands for Straight Edge which is a label for people who don't do drugs, drink, smoke, have sex, or do anything remotely risky. They use foul language to compensate for their lameness.
Straight Edge kids generally were unpopular as young teens, and were never offered drugs or sex. They grew up without friends with whom they were comfortable enough to have fun with.
Eventually they become tight-asses who see themselves as above the kids they envied as a child.
Normal Kid: Hey man, lets go to a concert!
SxE Kid: Hell the fuck yeah!
Normal Kid: My cousin can get us into the bar there!
SxE Kid: Oh... I'm not fucking into that fucking shit.
Normal Kid: Dammit, I didn't take you for a SxE faggot.