Alright, this is definitely a peeve to me. I haven't seen it often, but when I have it gets me.

When people roleplay in both third and first person. Like, they switch every other reply.

So the first thing they send could be:

Gwendolyn walked down the street, humming softly to herself.

Then you could send:

Marco waved when he saw her, running over. "Hey Gwen!"

Then they'd send...

I smiled at Marco, pausing my humming. "Hey."

And then the pattern would continue like that.

Why? I hate first person to begin with, but why would you switch your reply style like that?