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1.
The erection one has in the morning hours.
I woke up with the biggest piss fat this morning. My girlfriend thought she had excited me and decided to blow me. I think I accidently did a few wee drops in her mouth.
by Penis Master July 27, 2003
 
2.
Aussie term for a morning erection brought on by a full bladder.
don't jack it: it's a pissfat!!
by skirtlifter January 10, 2005