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1. When a surfer has the runs/explosive diarrhea and is waiting for the next set (of waves) too far from the beach to make it to a bathroom and "let's it go" while sitting on his or her board

2. A sex act where two wangs or sex toys are simultaneously inserted into a butt at angles so they come together in a point past the sphincter and the two wieners or dildos outline the shape of the front of a surfboard
Brodie was super embarrassed when he went back out too soon after eating Indian food and ended up with a rusty (surf)board.

I heard you and your buddy ran a rusty surfboard on your girl the other day. She must be super chill.
by DerHoffMan June 16, 2016
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