Green’s Dictionary of Slang

1. speaking incessantly and obsessively on a particular topic of little interest to anyone but oneself.

1991

E. Raymond New Hacker’s Dict. 158: flame 1. vi. To post an email message intended to insult and provoke. 2. vi. To speak incessantly and/or rabidly on some relatively uninteresting subject or with a patently ridiculous attitude. 3. vt. Either of senses 1 or 2, directed with hostility at a particular person or people. 4. n. An instance of flaming. When a discussion degenerates into useless controversy, one might tell the participants ‘Now you’re just flaming’ or ‘Stop all that flamage!’ to try to get them to cool down (so to speak).

2. using computer ‘bulletin boards’ and other communications links to circulate obscene messages, pictures etc.

1991		see sense 1.
1999		Guardian 23 July 7: Flaming. The vituperative insults and personal attacks common to email and newsgroups.