piss proud

(British, vulgar, by extension) Falsely proud, implying an outward display of success or virility belies a dubious reality.

(British, vulgar) Having an erection when waking from sleep or, more generally or metaphorically, a false or "empty" erection.

(British, pejorative, dated) Denoting an old man who marries a young woman, implying the only erection he could muster would be prompted by the bladder.