Armwrestling is and always has been a terrible idea. Even in my younger years I always avoided it like the plague. Well, all I can say is: I never lost use of my arm for a few days at a time because of tendonitis or worse.
When you're a big guy, everyone wants to arm wrestle you it seems like. There is so much technique involved IMO that it is easy for a much weaker guy to beat a stronger one. Strength as in strength in the gym. Whoever wins is certainly more functionally strong.