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I think O.O.C. Is Serious Business fits a little.
^ Seconded, possibly overlapping with a Bait-and-Switch. I'm reminded of an old episode of Family Guy where Quagmire the depraved satyriac gives Meg a meaningful talk about how fulfilling relationships are based on things like mutual respect and emotional connection.
Possibly related to Hidden Depths. Maybe a downplayed example of Crouching Moron, Hidden Badass?
Maybe Hidden Depths mixed with The Cloudcuckoolander Was Right?
Seconded.
Is there a trope for when a comic relief character in a Romantic Comedy, maybe one of the protagonist's Amazingly Embarrassing Parents, stops being Played for Laughs and gives the protagonist an earnest bit of insight/advice about romantic love that's relevant to their relationship with their love interest. Like in Friends with Benefits where Mila Kunis' mom stops joking about not being able to remember the identity of Mila's father and says that her dad was the only man she ever truly loved?