One of my weirdest bully headcanons is that Derby may have haemophilia.
Derby doesn't show up much in the story when it comes to fighting, he doesn't fight in dishonorable fight until jimmy beats bif, stays inside during Complete mayhem until jimmy goes to fight him, generally doesn't seem to participate in boxing at the club with his peers (although this just is the fact that leaders don't appear in freeroam) and he doesn't appear in the rumble, which is specially interesting due to the fact that its a mission, which could prompt leaders to appear, and it couldn't be because he doesn't care about Lola because other preps that werent involved with her do appear. Derby may just avoid fights when he can to due to the complications in his healing.
Also haemophilia is a genetic transmitted disease that can be caused by inbreeding, which is a trend among the preps.
After fights Derby stays bedridden for a while because of how ill he feels,and then his father pays the school so these little dissapearances arent reflected on his attendance records.
The Harringtons also keep details about Derby's health as secretive as possible, it would be shameful to let people know their blood isn't as pristine as they like to portray.
Ts is indeed a shower thought.