I would normally stop after two losses, unless maybe you lose the first two games. I think the more losses people get in a row, the more nervous/angry they'll get in the next game, which never really helps.
You'll eventually climb up, I never forget when I dropped over 300 SR in the course of two weeks and that was me not taking my own advice (and a lot of throwers/leavers). I think taking a break from comp sometimes helps too, maybe stick to QP for one night or play a different game entirely. I've seen some people on my friends list drop 200+ SR in one day, they play comp too much and don't know when to stop after taking a few losses!
Can't stop me, Legacy! Let's lose some more together!