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(n) the act of releasing fecal matter while performing anal with your girlfriend/boyfriend while the male genitalia is currently inserted in the anus.

Verb tense: muddy-submarined
Bro....my girlfriend let me muddy submarine her last night, she can't move now....great success!

Or...

Jim, my girlfriend just gave me a muddy submarine and now I can't walk or sit down.... not great success
by The Red October March 20, 2017
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