The most badass person who just doesn't give a damn
An infantry man whose gone balls to the wall is "grunt as fuck".

See that man not caring he's "grunt as fuck"
by gmangrunt February 17, 2014
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Extremely aggressive play with the female positioned in the Diddly Dog screaming GRUNT
I was enjoying a pie and coke whilst watching the footy and the girl said at halftime let’s grunt fuck.
by PIE&COKE March 18, 2019
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