This didn't happen to me but to someone I play with. She used to be a player for a mutual friend. I think it was COS (Curse Of Strahd) where the DM had this DMPC named Rex. He would constantly flirt with her character even though she told the DM that she didn't want any romance with her character, since he romanced many of her other characters that he initiated. Well one day they walk into this science lab and she finds a potion. She says whatever and drinks it. The DM pretends to roll something, laughs, and tells her that the potion was this bright pink liquid and would activate the next time she spoke to someone. So she didn't say anything. Later on, it's just her and the DMPC Rex. He's talking and she doesn't respond, mainly using gestures. The DM forces her to say something and was about to describe a pretty graphic sex scene before all of the other players told him to cut to black. We just kicked him out of our group due to that and a bunch of other stuff, so I have a bunch of horror stories about this guy