I've been using a version of this for a while, where I get a very satisfied feeling out of writing an angry response and then deleting it without sending. It's not that I train myself to write and then discard responses; I'd rather not write them at all and save the time. But when I catch myself having already written one, checking it before submitting, pondering what to change, I want to remember that I have the very satisfying option of deleting it all and backing out. (I just thought that this may easily appear foolish - what's the benefit of deleting if I've already invested the time to write it, and furthermore, perhaps I'm inadvertently training myself to attempt engaging more often in order to get the satisfaction of backing out? But the thing is, for me personally the costs of writing one comment or post are dwarfed by the costs of entering a spirited debate or a flamewar. Having entered the arena, I tend to obsess over the ensuing argument, rehearse past and future responses in my head, try to predict the reply I'll get and how I'll answer it - all this even for stupid and trivial arguments. It's a gigantic time sinkhole. So remembering and valuing the option of backing out at the last moment before entering the fray is on balance hugely beneficial to me).

Related: I used to have a much bigger problem tabling arguments, even if I really needed to be doing something else. (Especially pernicious if you're part of a college debate group where people think nothing of staying up til 3am talking, even if you have glassblowing class at 8:30am). I felt like saying "I really have to go to bed, or I'll burn myself in the morning" was tantamount to "You're so much better than I am, but I'm too much of a coward to admit I'm begging off." So, what I did was to visualize the worst thing that would happen as a result of leaving the fight. In one case, I imagined my interlocutor, D___, emailing all our friends to say "I was arguing with Leah about how well fleshed out the female characters in Assassins are and she ran away because she sucks!" One I said that explicitly to myself, it was pretty obvious that D___ wouldn't do that, and, even if he did, our mutual friends would think it was the email, not my going to bed, that was weird. And then I went to bed.