Someone worth knowing will take something someone with an obvious problem with you says with a grain of salt. If I heard for Person A that Person B is an idiot, but I know Person A doesn't like B, then I'll not be swayed by that.

That said, if it's gotten this bad I think it's time to talk to the coach or another adult in charge and get some mediating going.

And, this may change my advice, but why do you two have such a beef with each other?