1) The actual facepalm sound doesn't really sound good. It sounds like a snaping stick more than a facepalm. Something like the sound when you hit your teammate with the Disciplinary Action could work really well
2) Some classes had too long of a build up to the actual, for example the demoman does the "Ughh..." thing at the begging and if you want to show this on a killcam it could screw up the timing

Other than than a really great taunt