An old and very descriptive scouse expression depicting male masturbation.
Like the pouring of vinegar on fish & chips, with the bottle and it's bulbous head pointing down the vinegar bottle is shafted repeatedly in a downwards motion to release a tiny squirt of vinegar on every thrust, much like the male orgasm at the end point in which ejaculation is inevitable, coincidently producing a scrunched up face similar to one that has just sniffed vinegar.
Dave: that wank I had last night was lush
Paul: did your face scrunch up when you started on the vinegar strokes?
Dave: aye, it was like being in a chip shop
A method of swimming; you have front crawl, back crawl, breasts stroke, butterfly stroke and vinegar stroke. You prepell yourself through the water by girating your hips like your giving it to a woman.
You can prepell yourself backward using the same method...just by doing it on your back.