A guy that when using a urnal, gets so close to it, he practically looks like he is humping it. Usually someone who is insecure about penis size, shape, etc., so they feel the need to avoid all chances of anyone else seeing. Common in boys ages 8-16
While walking out of the locker room:

Guy: Did you see Ethan back there?

Guy 2: yeah, he's such a urnal humper! I thought he was going pee all over himself

Guy: probably just has a small dick
by Whitesoxfan69 April 18, 2011
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