you pu it on the internet, you're gonna get it come back at you.
Take naked photos? One day someone will put them online somewhere maybe somewhere "safe" maybe give them too a friend. Sooner or later they'll end up online, then someone will find those photos. They'll then post it somewhere that people take an interest in such things. One of them will find you. Then it's all over.
They'll post pictures to your friends, family, work collegues, educators, governors, anybody they can get mail addresses. They'll raid social networking sites, create fake accounts, they'll invest a whole night in wrecking your world. If you provide epic lulz maybe they'll spend a few nights on you. If you provide truely epic lulz they will spend weeks on you.
The same stands for anything else you post, events at drunken parties are there for all to see, being unfaithful, stealing office materials, bad mouthing foreigners, so on and so forth. If you put it online, one day it could come back and bite you in the ass, and you have nobody to blame but yourselves. Course the Oxford professor, law enforcment and potential employers do it for a "good" reason, most people will just do it for a laugh.