Today I learned that there actually are shirts which ask others to hit you.
If I wear one of those shirts, and someone actually hits me, are they still liable? I'd guess that they are, but can they argue that my shirt limits their liability?
I have no particular jurisdiction in mind.
Outside of the context of sport fighting, one cannot consent to another intentionally applying force that causes serious hurt or non-trivial bodily harm: R. v. Jobidon, [1991] 2 S.C.R. 714.
And consent would be be irrelevant in a charge of criminal negligence or manslaughter, if the act was to escalate that far (R. c. Deschatelets, 2013 QCCQ 1948, para. 175-77).
While there are some vary limited circumstances where you can consent to contact that may cause harm (e.g participation in a contact or combat sport, medical procedures), wearing a T-shirt with a (not very) funny slogan isn’t one of them, and isn’t even consent.
Just like wearing a T-shirt with the slogan “Kill all the lawyers” isn’t an incitement to violence.
I suggest the answer may be "yes, but no jury would convict him." As others have mentioned, wearing a shirt that may be a joke, unfunny as it may be to most people, it's hard to see how that would be considered sufficient to constitute consent, legally. OTOH, if someone did such a thing, and requested a jury trial (as one may, anywhere in the U.S., at least), I suggest that most juries would refuse to find the puncher guilty, along lines similar to "if he's stupid enough to wear that shirt, he deserves to get punched," or, at least, "someone who takes him up on it shouldn't go to jail."
NOTE that, again, as mentioned previously by others, this entire discussion is assuming there is no significant injury. If the assailant were to punch him "in the gut" hard enough to rupture his spleen, and the victim perished (this is how Harry Houdini died), some jail time would be expected.
