I bet she , your friend, has a similar perspective about how frustrating it can be to ride with Kiwi, who insists on total obedience all the time. It takes the fun out of a ride!
I guess I am the bad friend too, lol! One of my horses is AWESOME, and is always among the best behaved horses in the group, if not the very best behaved. But you know what? If a horse is giggy, or slow, or hyper, as long as it isn't really creating a danger, I just let it roll off me. I think agree with the quote above, it DOES take the fun out of the ride if you have to be "perfect" all the time.
My horse who actually is close to perfect, is also very slow, and it would annoy my friends with gaited horses because I would always have to trot to catch up, and that would get their horses all excited. My horse is pleasing me and doing as I ask. If trotting up excites their horses, then maybe it's THEIR horse that needs the training. Know what I mean?
In other words, if my horse is doing as I say, and isn't a danger, but he has to trot to catch up, and the other horses get excited, maybe it's the other horses that need the training. So I dunno, I guess I would enjoy riding with your friend with the "bad" horse, because it just wouldn't bother me. And if the horse getting rammed were actually annoyed, I'm sure it would kick, or at least threaten to.
I do think it's bad behavior to let your horse get too close to another one, and especially it your horse is ramming into another one, but all in all, if it's really a problem, then the horse being rammed will give dirty looks and threats at some point.
I have ridden with one lady who is so tense, and so worried about her horses being perfect, that she is tense, mad at her horses all the time, and her horses are nervous wrecks. Sometimes you just need to relax and have fun.
Riding should not be an experience that makes you mad. It should be fun!
Because of my relaxed attitude, I also have a reputation for ridding jiggy horses that other people would not enjoy. But that's okay, they only have to please me.
I did finally buy a gaited horse to keep up with the gaited horse folks, but I'm sure my QH friend will find her annoying, because she is rather go-y and jiggy at times. But hey, you can't please all your riding buddies all the time. But now I have a fast horse AND a slow horse, so I am prepared for most occasions.
But relax and have fun, that's what riding is all about. And if the "bad behavior" bothers you, then maybe it's best you ride apart.