What is "piss proud"

a. 1 (context British vulgar English) Having an erection when waking from sleep or, more generally or metaphorically, a false or "empty" erection. 2 (context British vulgar English) (by extension) Falsely proud, implying an outward display of success or virility belies a dubious reality. 3 (context British pejorative dated English) Denoting an old man who marries a young woman, implying the only erection he could muster would be prompted by the bladder.'''2003''', Mark Steven Morton, ''The Lover's Tongue: A Merry Romp Through the Language of Love and Sex'', 4 (context rare English) paruretic.