Anything that is fun. It can be used as a noun, adjective, or verb if you're feeling adventurous.
When spelled backwards or with an "anti" added to the front it has the opposite meaning.
"Im going to buy some treatsies."
"Want to smoke a treatsie bowl?"
"Im gunna treatsie you until the cows come home!"
"You're the treatsiest person I know!!"
"I love you treatsie."
"Organized religion is an eistaert!"
"No more ganja, anti-treatsie!!"
She is the sweetest person ever! She seems shy at school or when you first meet her but when once you get to know her, she is the silliest, funniest, and most energetic person ever. Not to mention she is drop deadgorgeous!