now, we all know who murphy was and how he contributed to the world. therefore, in absolutely all cases, murphy must be seen as an ally, not as an enemy. so listen to your ally's advice: at some point, that certain character will engage you by bestowing all his said stupidity, ignorance and lack of humour upon your presence there. maybe it was something you said, maybe it was his lack of medication, the truth is that it's virtually impossible to prevent this: once you're engaged in a comment exchange with such a person, you're bound to bask in a sludge of putrid neurons, freely pouring from that person.
so, this is when the prophylactic block occurs: before the engaging. you see their comments, you realise they're as dumb as a doorknob, it doesn't matter if they have a hot profile picture (actually, it's best to not even open their profiles), it doesn't matter if you've not been laid for quite some time and you think they would be your sure-fire solution, you must block them. sometimes it's tough, but it has to be done. it's like sleeping with a hooker when you know you're flat broke and don't even have a condom: say "pass" and everybody will be happier.
all you have to do is make sure you don't think of such morons as people who could be your online friends. if you've already lowered yourself to that point, it means that you have much more serious problems to deal with and you've already lost the war.