To put your balls on another's face; to teabag someone.
Fred: "So did you slap her with the nuts?"
Bob: "Yeah, I put $5 on it."
Given as a sign of full approval. Derived from the voting system on Threadless, it's become a show of love for a remark, design, person, etc. Primary use is in the Community Forum, but could extend to the "real" world.
Blog entry: Here's a picture of me with my new mohawk! I may end up losing my job.. but doesn't it look awesome!?!