Not on purpose....ever. It's a bit childish. Have you ever seen a picture of someone who's been hit by a ball?
This works for me - I figure you can't always see the next three or four groups in front of them (no matter how it 'appears' to you) so the slow down might not be their fault. Then you have a group frustrated at the slow play in front of them and an ******* is now hitting into them.
Once you hit into them on purpose, it doesn't matter how they play - it's your fault. No excuses. You are in the wrong no matter what.
However, if it's slow and were all catching each other, I'll always let the group behind me know if we're being backed up too and there's no reason to play through. That's all it takes and everyone is friendly and commiserating with each other. if there is a gap, they can play through, or, play along for one hole to get in front of us, etc.
Slow days, I'm also a fan of small groups catching each other and combining - it's amazing how many people just refuse to do that. For that matter, if a 4way is sandwiched by two 2-ways, even on a slow day, it makes sense to send that 2way through as long as they join with the other 2way asap.
you gotta talk, quiet and stewing is what children do