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Trench fanny is when you have a splash in the sea fully clothed and proceed to walk around all day with sopping knickers and a good ol’ chafe.
“Oh crikey, I love swimming in the sea, but now I’ve got trench fanny!”

“Susan, I can smell your trench fanny!”

“Damn, I forgot a spare change of clothes... I’ll probably get trench fanny again.”
by FlappyFanny July 23, 2018
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