Sus

Short for "suspect" or "suspicious", but is also used to mean lame, normie or mainstream.

Depending on the context, it can kind of mean anything describing something.

Example 1
A: "They like Gossip Girl alot."
B: "Shit, I told you they were sus af."

Example 2
"Liking Green Day became so sus. It's sad, 'cus they're really great."

Example 3
"They're acting sus."

Example 4
"Drinking lean became so sus all of a sudden. Now with xanax culture rising and all."