A good thing in a brainstorming is you and your partner in team have an agreement about something. All of you must deal with the things before and after the forum runs i.e the rules, the value, the atmosphere, the do and don't, and so on.
Why all is necessary?
It is very helpful to make the brainstorming always on the track: the right direction. A conducive situation.
Just avoid to fighting or wasting time and energy for nothing
Remember that you have to save your energy before really fighting with client :)
And what is the bad thing?
It happens if you all are selfish; try pushing each idea as a mandatory must obey which is not relevant regarding to the objective of that brainstorming. In result, you or others probably will lose control and judge any idea from other as a meaningless thing. Rubbish.
It's not a kind of World War...so just relaxed.
Treat the forum as refreshing so you will get the gain.
Don't insist someone to accept your idea if someone else has a better one.
Calm down. Be positive. Be low profile.
Everyone needs a peace of mind circumstance.
Why not wear this T-Shirt with the following copy to express yourself in humor way :)
PEACE OF MINE