piss proud

Meanings

1. Having an erection when waking from sleep or, more generally or metaphorically, a false or "empty" erection.
2. Falsely proud, implying an outward display of success or virility belies a dubious reality.
3. Denoting an old man who marries a young woman, implying the only erection he could muster would be prompted by the bladder.
4. Paruretic.

Etymology

From piss (“urine”) + proud. Appears in Francis Grose’s A Classical Dictionary of the Vulgar Tongue (1796): : “PISS-PROUD. Having a false erection. That old fellow thought he had an erection, but his — was only piss-proud; said of any old fellow who marries a young wife”.