Absolutely nothing, because I’m not stupid enough to think men can’t, or shouldn’t, knit.
Men have always knitted. It’s likely that knitting was invented by shepherds – men herding sheep. In the medieval era, men completed a 7-year apprenticeship to become professional knitters in men-only guilds. The Moorish knitter who created the silk pillows in the grave of Spanish prince Ferdinand de la Cerda was probably a man:
The first knitting machine, in 1589, was invented by William Lee, a man. Sailors and soldiers have knitted, at sea and in the trenches. Most haute couture knitwear designers, even in recent history, have been male:
My uncle became a globe-trotting mining engineer not because of his education, but because he could cook, sew and knit, and therefore could be sent to uninhabited regions of the world without female support. My father, a lorry driver and former amateur heavyweight wrestler, won prizes for his lace knitting:
My younger brother learned to knit before I did, and can still knock out a decent pair of socks.
So, if I saw a man knitting in public, I might ask what he was making or which pattern he was using, ask what his Ravelry name was, and give him mine.