Mutilated prisoners become your foes, so you can still duel them (but I'm not sure if that "stress relief" event works on foes).
Mutilation does not make you foes, strangely enough. The "foe" status is only caused by opinion modifiers that are marked as crimes. This is not to be confused with imprisonment reasons.
(The game files mark them "crime = yes" and "prison_reason = yes" respectively.)
There aren't that many crime/foe opinions, and most are not easy to produce at will. The most easily reproduced one is probably attempted murder - you can get that one by planning a murder plot and having someone blab. This will make you a foe of the target, and possibly of their spouse, siblings, children, and parents. So plan a murder plot and invite only drunkards.
Another one is to divorce a woman, which makes you a foe of her and her relatives.
If anyone wants to see them all, they can go to the file common\opinion_modifiers\00_opinion_modifiers.txt and search the file for all instances of "crime"
PS. I am aware how weird it is that having someone cut off your arm, leg, or even carve off your entire face does not make you foes and give cause for a duel, but divorcing your sister does. I didn't come up with this stuff.