The vinegar like sweat residue that builds up on ones gussett on a hot summers day. Most common on men found on the 'Quillum" valley between ones scrotal sack and arse. Has the distinct and unmistakable pungent hue of a highly Sarson seasoned portion of chips.
What's that smell on your fingers, have you been fingering the jar of pickled onions again?
No my good man, one has scratched one's nuts and this my friend is Gusset Vinegar.