It's been going on for millennia, but now we have a word for it: negging.
The idea is that instead of saying nice things to fanciable girls (or boys) you insult them. This is supposed to make you look honest and intriguing and independent - even, possibly, amusing. It might well make the targets of your insults feel insecure, too, and less inclined to assert themselves. And then you're in.
The trouble is that the line between the sweetly teasing and the brutal is wafer-thin.
'Did that shirt shrink in the laundry?' might pass as a very obvious joke - it certainly acts as a warning to avoid the perpetrator, unless the victim has a high tolerance of very obvious jokes - but 'your roots are showing' is quite likely to be crushing and a put-off unless the victim's ego is in really excellent order.
Still, you might just get away with negging if it's disguised as showing an interest...
'I really like that dress but, I don't know, perhaps you should have gone with red shoes.'
...but I doubt it.
The other sort of negging involves leaving negative posts on a comments board. Sometimes it's genuinely helpful, but mostly it's tends to be a display of the writer's unhinged, twisted and bitter mind.
Still, even that can be quite amusing to a reader, from time to time.
Thing Not To Do Today: negging. This is, presumably, short for negative. Nec is the Latin for not.