Yeah, I reply with a bold reply, as rude, yet as 
sarcastic as possible. Because, I learned to 
regard flame mails as entertainment.
Like, when someone gets very pissy in an email, I 
tell them: "Have you every tried anger management 
through sexual intercourse? Sex is supposed to be 
10 times more efficient than valium! Ah, oops, 
sorry, I forgot that according to the niveau of 
your previous email, you cannot be older than 6 
yet! In that case I recommend your mama's breast."

One shouldn't take pissy emails seriously. Always 
give the author the impression that it amused you 
and ridiculed them. You can also try pissing them 
off more by replying sarcastic stuff like "There 
there, did your mama not give you enough 
attention that you try at me now?" and watch as 
they explode XD

^^
Anna