Doh#1 funny for you, not for your uke. Maybe she can laugh about in a few months' time.
Doh#2: inappropriate atemi - bad boy. But shit happens
Doh#3: try to talk to Sergei. Even Russians are able to listen. And later you have to learn to take ukemi, i.e. take the torn arm and leave with a smile
. Really the softer you are the less he can hurt you. But there is no need to feel permanently like your uke #1.