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When fucking and you get brewers droop or can't manage anything more than a slack-on, one is required to 'thumb it in'
As seen on many porno's
"Fuck me hard Liam", "sorry petlamb, ive gone all soft i'll just have to thumb it in"
by Diamond Dave April 28, 2004
To deliver information of some importance via text message. Akin to "phoned it in"
"She told me she was pregnant in a text message. Way to thumb it in. "
by Fungo December 24, 2009