If you feel like friend or acquaintance is intentionally doing something that gives you anxiety how do you know whether to let them know?

I wouldn't want this person to feel anxious or pressured themselves to change their behaviour.

I wouldn't want to give them the opportunity to lie or gaslight me into thinking I'm just imagining what's happening, if the thing they're doing is intentional.

Opening up to them means they know what affects you so in the future they could use it as a weapon even if they say they're sorry about doing it or something.