alt.flame is a newsgroup dedicated to the kinds of arguments that are frequently discouraged on other groups – the more vicious, the better. According to an Everything2 poster, it was "Often encountered with a helpful Followups-To: alt.flame header, which translates into 'You want to take this outside?'"
During Looniverse Adrift!, while the Looniverse was careening across the Usenetverse, it passed through alt.flame. Net.ropolis was temporarily transformed into a dark landscape, stinking of brimstone, with great gouts of flame shooting into the sky, and the citizens turned into demonic beings of pure hellfire.
When Fan.Boy and Retcon Lad traveled to this group to capture Firewall, it also appeared as a hellish landscape consumed by flames.
Not surprisingly, alt.flame is still very much active, and can be read here.