It's not really working together that's fun, it's more fun to use the other person to your advantage (if you both agree not to kill each other for being selfish).
Throw the guy at an enemy, get some laughs, and the same thing happens to you. If you don't take things too seriously, you'll even laugh when you die.
And it's not like working together sucks.
When Shariq and I (try to) work together in New Super Mario Bros. Wii, it has its benefits and you get some laughs out of it too.
If you really hate getting in each other's way, you should try communicating more (that's really why I always die or accidentally kill Shariq when I play, I never tell him what I'm gonna do and it's bad for both of us.)