I'm kind of falling on the side of thinking "it's sucks" is not that bad. Don't throw it all over the place like it doesn't mean anything, but I can think of several situations where it would completely make sense. (A nasty bully, a kid who's been pushed to the emotional breaking point, ect.)
As for using, "like," a lot, it might happen in natural speech frequently, but writing it too much, imo, makes it sound like you're trying to imitate valley girl speak. Most adults I hear using it are more often stumbling for words. ("Well, it's like this.. I was trying, um, like trying to fix it, and it then went like... bam!") Or, they're retelling a conversation, "I was like, 'Could you move?,' and he looked at me like, 'Well, I could, but I won't.")
I don't think, "I totally get it," dates itself as much, only because the phrase, "I get it," has been around for a while. If you've got a character that would use the phrase, "totally," then go for it.
To me, the big thing to remember is that not all tweens/teens speak the same way. And if you try to force what you think are the "in" phrases on your characters, it'll show. (I can think of a couple MG/YA novels that suffered from this. Didn't make them bad novels per se, but they would've been so much better with more natural dialogue.)