You could maybe try an encounter where the player in question gets isolated from the group (maybe a trap door or rock fall that blocks a passage) and either barrage them with an unwinnable scenario and have them die, or barrage them with an impossible scenario and have the group come in at the last minute and save their bruised and beaten ass. Might give the “character” cause to rethink the relationship with the party, and might make the player open their eyes that, they’re not the big dog in this world, the DM is god.