I pretend there's a big secret game of whoever talks first loses. It's the truest rule to this stuff. If someone's trying really hard just stay mute, pretend to be a noob getting lucky and adopt the most irritating playstyle you can think of. No taunts or teabags, those give your intent away immediately. Most 2015ers or whatever we're calling the current crop of online players have really bad personalities but they also rely greatly on having preplanning responses to things like you mentioned so it really throws them off and turns them into the aggressor if you stop giving them anything to bounce off of.
If you really have to talk though (Why would you want to, have you not met the average online player nowadays?) you could try something that comes off more like an eyeroll or disappointment in them. When you say you don't care they think "That's what someone who cares WOULD say" so you need to act apathetic instead of outright stating it.
Still waiting on that third threat