'Urgh!' I said as my friend described the behaviour of a couple at a recent dinner party. 'Kissing her and fondling her feet. That's revolting.' What made it worse was that neither was on the younger side of 40. They were older, wiser, and should know better than to indulge in such public displays of affection. If they'd been young and in love it was forgivable, we decided. After all, the world loves a lover - as long as they're young. But on the MTR later, I had second thoughts when, in the rush-hour crush, I was forced to stand barely a breath away from a couple of kissing teenagers - so close I could hear the slurps and smell the mint freshener. The pair were oblivious to their fellow travellers, who, like me, averted their gaze or pretended they weren't there. There are times and places for this kind of thing. Park benches, cinemas, sofas in front of the television, dark corners in nightclubs and behind bike sheds, I can accept. Rush hour on the MTR, definitely not. Perhaps the MTR should post 'no petting' signs alongside the 'no food and drink' ones on trains. The public swimming pool I visited as a child had one that showed a cartoon of a couple puckering up with a line through them and the words, 'no petting'. At the time it puzzled me: I wondered who took pets swimming and what that had to do with a kissing couple. But there's one display of affection I abhor even more. It's so unsociable and lacking in courtesy that it should carry a fine on a par with spitting, littering and letting your dog foul the pavement. Anthropologists may argue that it's a courting ritual that harks back to the days of the cavemen and could be a form of mutual grooming. In my experience - and I come across it with alarming regularity - it appears to be initiated by the female, who pins down the male with a look in her eyes usually seen only in predatory animals moving in for the kill. I've seen courting couples go at it in all manner of places: trains, parks, cafes, public swimming pools. So gross do I find this particular display of affection that I'd ride the Island Line with a carriage full of kissing couples or be seated at a dinner party in the middle of some foot-fondling oldies if I could escape a close encounter of this kind ever again. What is it? Public pimple squeezing. Come on young lovers: save it for behind closed doors. That really is revolting.