Random act of random kindness
The true story of a true rark: Once long ago, a girl was trying to win a stuffed animal out of the claw machine but ran out of change. While she, in despair of already wasting $4, put change inside a change machine, another girl won the stuffed animal out of the claw machine, and gave it to her.
Random compliments, hugs, free items, etc. all fall under the category of a "Rark"
If someone runs up to you and randomly hugs you, an appropriate thing to reply with is "Thanks for the rark!"