I've learned that when my friend's husband decides he's going to come out with us on a long ride he is very, very annoying, with the gift of riding 3/4 of a wheel-length behind you so that you know he's there, but can't see him properly and can't anticipate what he's going to do next. I also learned that when you need to pass a slower cyclist he intuits this and chooses that very moment to give one clang on his bell and pull past you leaving you running out of cycle track rapidly.
He learned that while I might seem to poddle along relatively slowly (I did - my friend and I had the whole world to put straight while we were out and there was much to be chewed over), I am fast enough up an incline when I want to be and if I don't want him to overtake me, he's not going to get it all his own way.