Character speech

What is your biggest pet peeve about speech in fics?

Personally its when people write two different characters speaking in the same paragraph. Especially when there is no indication of whose speaking- 'she said' 'he said' etc. I quickly lose track and have to figure what's going on before I can carry on reading. Totally breaks story flow for me. If the story is short I carry on reading. Anything 5000 up or multichaptered, I click away.