[17C] a miser, a mean person, thus piss vinegar, to be mean.
(alsogravy strokes) [? one ‘puts a bit of vinegar’ into them; note Barry Humphries, The Traveller’s Tool (1985) in ‘Les’s Large Appendix’: ‘The penultimate phase in sexual connection when the active partner experiences a facial rictus similar to that produced by drinking vinegar (information supplied by a doctor)’]
[1970s+] the final thrusts of sexual intercourse; used fig. of a train in cite 1960.