I let up against my friends a lot. Being social while still playing competitively is much more fun than turning into robot trying to destroy them. I know it hurts my game but the tradeoff of having a good time hanging out with my friends is worth it.
True friends will applaud your skill and will be proud of you. I bet they'd be fine with it if you gave them a spot. You don't have to play like a robot. In fact I try to never play like a robot, even when I'm in tough competition.
You work too hard at your game to train yourself to let up, and that's just what you're doing every time you do that.