Powerplaying: When someone plays the characters of another roleplayer without permission or mutual understanding about acceptable boundaries between the roleplayers involved.
"Ew. Did you check to see what date this raw milk expires?"
"Yeah, what happened?"
"I found a curd."
"Did you shake it?"
"No."
"It's the cream. The fat floats to the top."
"Oh, I just thought it was Bridgid's backwash the first couple of times."
"Wait, why didn't you say 'ew' when you thought that?"