Jack is perfectly aware that Dean can’t stand him. He flirts with the elder winchester mercilessly, well flirts with everyone that way, but more so when Dean is present. But he also know’s Dean’s weakness for pie and likes to sneak them into bunker and surprise him. So Dean has no idea where these pies are coming from, but he’s grateful. And one day he finally says “I could kiss whoever keeps bringing these pies.” So Jack leans in and snogs him.