1)An item of clothing often associated with a person is commonly either wets the bed or has wet dreams.

2)An insult for someone who is boring or may have spunked themselves in public recently.
Man 1: Haha, did you hear about that guy who has wet dreams every night?
Man 2: Jees! What A-Pair-Of-Damp-Pyjama-Bottoms
by Guy Whitaker June 12, 2009
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