When it comes to anti-heroes, there are few characters that emphasise the 'anti' part as much as Lobo. There are very few Lobo comic where he isn't actively destroying the universe one unfortunate soul at a time - and when he's not, it's only because he's preparing for an event that is all the bigger.
All this in mind, the only difficulty with Lobo and his terrible deeds is figuring out which is the very worst, because he's carried out so many simply awful acts that it's hard to put your finger on exactly which would be considered the most depraved. With a man who has killed all his own children, killed all his own species, and at one point even killed himself, there's no shortage of moments to pick between - only the sinking feeling that maybe Lobo should have his anti-hero status revoked at some point in the near future.
If you're in need of a hero that amps up all the bloodthirsty wildness of Wolverine or the Punisher, Lobo is your go-to guy. If you want a character with morals? Well, you might want to give him a miss, for the time being.