For those of you who don't know, in 'net lingo, flaming is the (usually uncalled for) large-scale verbal berating of a person for having an idea or opinion that differs from your own. It usually contains lots of 4 letter words, wonderful mental inagery, and threats of physical harm if the opinion/idea shows up again.
Anyways, this practice often ends up making the flamer look stupid, and making the flamee, usually a newb, or other inexperienced person, feeling angry and hurt. (face it. stuff people on the internet say affects you the same as what anyone else says.)
Flaming has it's roots in the early days of the internet. It takes the place of things like ritual hazing in fraternities and other clubs/institutions. The same mindset of "since i've been here longer than you, i must somehow be better/smarter/more-attractive-to-the-opposite-sex-even- though-i-have-no-life-because-i-stay-on-the-computer-all-day-and-never-see-a-girl than you".