>Well, at least when me and other developers are making a proposal to the same customer, the other developers aren't my best friends. But maybe I should have choose a better word to describe the situation. Let's replace the word " enemy " by " competitor ". Is that better for you?

Absolutely!

Just as a matter of curiosity, if you and a friend of yours each propose a solution to the same customer, are you not still friends with that developer? Competitors yes, but still friends?

Personally, I think the professional attitude, which I try to adhere to, is pretty much as Dragan said. Don't put anyone down by using belittling terms at any time, but especially not in front of the client and play fair. I don't always succeed, though but that's because I'm not perfect just like everyone else.