I'll try to explain what Cobalt meant.
If they're trolling sleazy, stupid dickheads on here, they're probably looking for certain criteria in the subject matter and the main text. For example, if you've been really sleazy in the message and sent a picture of your cock, they'll probably bite and see what else you'll stupidly send (face pics, full body pics, email addresses, phone/snapchat/whatsapp etc). They'll troll your contact details, may even arrange a date and make you drive hours just to waste your time.
Then they'll show all of this to their friends, post it on here, post it on Facebook/other social networks and laugh at how retarded you've been...like this: https://www.youtube.com/watch?v=fqWjvlrZsnY
Moral of the story - always be careful who you speak to on the internet and if you've got any brains whatsoever, let other people send naughty pictures of themselves but never do it yourself.
That's why when I was single, if I was ever looking for a quick shag, I'd always target chubby, single mums who were a bit stupid and lacked confidence. Much more likely to send nude pics without even knowing who I was + shag me on a 1st date. Very attractive and particularly intelligent girls are't generally going to fall for this approach with someone they don't know.