it all started because dennis was sick of mac wearing old polo shirts with ties any time they went out for their monthly dinners (or any formal event, really) so dennis made the threat to refuse to be seen with him at any events if he wouldn’t wear something more classy (to which mac argued that he could be classy! he could totally be classy if he wanted to!). they went clothes shopping and dennis told mac to pick out something to prove it, and of course everything was tasteless and terrible, so dennis took it upon himself to find him something new. mac doesn’t hate it as much now a days, because he just likes being able to spend time with dennis, he couldn’t really give a shit about the outfits.