It's a neat idea, but after too many sarcastic, "clever", trying-to-be-funny, defensive, et al emails in my career I have a simpler heuristic. If I have to ask myself "should I send it?", the answer is no. Leave it in drafts (with no one in the to: line!) until either things have cooled down and I delete it, or there's more perspective and it's actually ok to send.
I have too many fails to tell, but the worst ever was an email from a middle manager I didn't know at BigCo, cc: upper management. It blamed an issue on my team at the time, and I took it as an attack. For once there actually was no issue, and in my reply I managed to subtly rub in that they apparently didn't understand how their own dept. worked. CC: upper management still of course. It worked too well, and the person called me crying an hour later because they looked like an idiot to the big cheeses. As soon as we talked on the phone, they became a real person to me, and I felt like the utter dick that I had been.
Moral of the story, there are real people with real feelings on the other end of your words. It's almost never worth it to be a dick, slightly off color, or sarcastic, save that for in-person ;-)