I generally don't yell "hold your line". What I will do (did at Limerock this year) is roll up to the guy and say it to him in a lower, calmer voice. I put my hand on his back to steady him so he wouldn't run into me. In other words it's a real directed comment, not something yelled out arbitrarily. The guy apologized so he gets a pass from me for a while. I just look out for him.
On the other hand I screamed at a guy three times in the last race I did. Like screamed at the top of my lungs, which I honestly don't remember when I did it last before that, and three times in once race, maybe in the early 90s. Absolutely wacky rider. Ends up he's an ex-pro but man, what a lunatic. Pushing, shoving, almost taking himself out because he's pushing so hard (swerving a couple feet to keep himself upright), trying to crash others… and not in any kind of crucial point of the race, just random laps where someone got him mad. Pointless aggression. He ultimately got DQ'ed but still. A friend of mine told me, oh, he's crazy, there are like 5 guys I avoid at all costs and he's once of them. That friend's been racing 25 years so that says something.
A friend of his who is a (different) friend of mine said, "Well, it's M40+ and it's always crazy in M40+." They used to be teammates, my friend's been racing almost 30 years, he started as a Junior just after I did.
I probably posted the above stuff before, or else I'm remembering messaging my friend, so sorry for repeating it if I did.
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"...during the Lance years, being fit became the No. 1 thing. Totally the only thing. It’s a big part of what we do, but fitness is not the only thing. There’s skills, there’s tactics … there’s all kinds of stuff..." Tim Johnson