When someone you know is about to have their life permantly, or for a very long time, ruined and you do nothing to prevent it or if anything you encourage it.
Girl: Oh I'm really happy
Guy thinking: Haha, her new friends will grimfuck her very badly
by Toothpaste Salad January 21, 2009
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When someone nods yes with a smile and then turns around to ignore everything they just agreed to do.
BOSS: Hi Bill! You get those TPS reports filed by Friday. We have a serious audit coming up next week and need it done.
BILL: Sure thing, boss! *smiles* *grins*

1 week later:

BOSS: Bill? Where the fuck are the TPS reports?! We're being fined by the SEC! You stood there and grimfucked me last week!
by Protonix February 22, 2016
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