How do you describe to an employer or a training manager you aren't a team player?

I think it's all about the emphasis you put on this in the way that you put it to your boss. By that I mean you don't won't to focus on the negative and instead try and give it a positive spin. By saying you don't work we as a team it's not going to show you in a very good light. Instead tell him you find you work best alone and by working alone that's how to get the best out of you. And then of course you've got to back it up, if you get to work alone show your boss that they made the right decision by backing you with what you wanted. Make your manager feel they've made the correct decision and managed you well.