Yes, sulk is a Scrabble word!
...and is worth 8 points in Scrabble, and 10 points in Words with Friends
sulk
Verb
1. Be in a huff and display one's displeasure
Noun
1. A mood or display of sullen aloofness or withdrawal
What Scrabble words can I make with the letters in sulk?
3 Letter Words
2 Letter Words