I'll share a little trick I use if and when I'm playing for someone. If you screw something up, and feel you must make a pissed off/upset face about it, just close your eyes and everyone will just think you're really getting into the song.....and then after you think about how you just made this real serious "getting into it" face through part of a song that is everything but serious/emotional, you'll probably laugh at how silly you must have looked and forget about the screw up.