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An insulting phrase used in glasgow, quite possibly in other scottish cities too.

Pump: verb. To have sexual intercourse.
Yer Maw: noun. A slang way of referring to another person's mother.
Pump Yer Maw: To have sexual intercourse with another person's mother.
Past tense:
"Awwww mate, ah pumped yer maw last nite"

Present tense:
"Awwww mate, am pumpin yer maw right now"
(possibly talking on the phone)

"Awwww mate, am gonnae pump yer maw the nite"
by HAC May 09, 2006
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