On Fri, 16 Mar 2018 19:19:54 +0000, Peter Dunce [BrE] wrote:

It might have something to do with shirts.

The OED entry for "shirty" point to this use of "shirt":

"to get (a person's) shirt out", to cause him to lose his temper.
"to keep one's shirt on": to remain calm (orig. U.S.).

Perhaps, only perhaps, that might refer to a person removing his shirt
to fight.

Peter Hucker will only remove his pants to make you suck his cock time and
again, Dunce! BG