Giles and Buffy in “The Pack”

Xander's taken to teasing the less fortunate?

Uh-huh.

And, there's been a noticeable change in both clothing and demeanor?

Yes.

And, well, otherwise all his spare time is spent lounging about with imbeciles.

It's bad, isn't it?

It's devastating. He's turned into a sixteen-year-old boy. Of course you'll have to kill him.