Forget the terrible 2’s, suit up for the exasperating 3’s. Good luck.

A possible trick in the car might work once or twice until the little snicker figures it out. : Give the snicker something it likes, if safe and applicable, like a slowpoke sucker, once in the car immediately take away the sucker, stand next to the child seat, should draw in the child for strapping in. Return the sucker and if necessary remove same if the child becomes overly clever again. Yep, the old carrot and stick leveraged approach but it could help to save your mind and you will need that for the perilous 4's.