What is that one thing you want to tell your co-founder but you rather not to?

One thing about my co-founder, is that it is really hard to get him start doing things, until the last min. Though once he started, everything is fine and the quality of the work is impeccable. But I really dislike chasing him on deadline, especially I don't want to get into a fight with him, which drives me crazy. What about you? What is that one thing you can't stand but you decided to keep your mouth shot?