I don’t have many headcanons for these two, and I don’t really think either count as ‘cute’, but but one of the ones I do have is that Mugman got a little jealous worried about his brother dating an oversize plant that did try to kill them not too long ago and would follow them around the first few dates, much to the couple’s chagrin.
The other I have, which, I think, covers the second ask, is that after the brothers beat the devil, local kids who wanna try to prove their badassery try to fight the boys. Mugman usually denies these when he’s alone, while Cuphead...does not, and despite Cagney’s sweet appearance most of the time, he is totally up for a scuffle and often joins in!
Unfortunately, most of these fights end up like this:
it’s almost like fighting a against a pointy tooth flower and a cup with a charge shot isn’t the best plan or something!