So we all know how Matt is a precious masochistic lil cinnamon bun with an adrenaline addiction and self-destructive tendencies, so he probably does lots of bad things like goes to BDSM clubs and picks up creepy weirdos or over zealous, undereducated kinksters who will ignore things like "safety" or "boundaries" and give him the pain that he wants.
Foggy knows, to some extent, and is very concerned, but Matt is an adult, and can make his own choices, and he's fine with it. Until one day he comes over to hang out with his best friend and Matt is just wrecked. The person who dommed him caused him some serious injuries and he's in sub-drop and all alone, so of course Foggy comes to the rescue and patches Matt up, and makes him some cocoa and lies with him until he feels better :D
Up to you if it goes on past that :)