(1) It can be a noun!
(2) It can be a verb!
(3) It can be an adjective!
(4) It can be an adverb!
Pretty much, it can be used in any context at all. It's as openly used as fuck
1. He's so tall...It's gotta be from the sexin.
2. And then I was all like *sexin* and ran down the street.
3. Look at that tall, sexin, awesome guy walking down the street.
4. John walked sexinly down the street, machine guns ready to go.