Refers to a stero-typical middle age Jewish male. Would generally be a Tottenham fan who likes Bruce Springsteen or pink Floyd. Favoured apparel would be a hard rock leather jacket worn as often as possible generally from some where non-pronounceable. Might note often how he is still with it and can handle himself, not out of choice but only when needed.
Would apply to most tracksuit wearing deli-shoppers in my frequented parts of North London. Note this would be the only time a Melvyn would need such apparel. I can already see a majority of my friends exhibiting the first traits of Melvyndom.
That fella over there, in the hard rock bahamas jacket, buying all that smoked salmon and herring is a right Melvyn. Look at his tracksuit.