expression, ichidan verb
conceited; stuck up; full of oneself; cocky
Colloquial contraction of 背負っている, literally 'carrying on one's back', used to describe someone who is acting arrogantly or overly proud.
あいつ、最近しょってるよね。
That guy's been really full of himself lately.
ちょっと褒めたらすぐしょってる。
Give him a little praise and he gets all cocky.