Typical Crossfitter:
Learns how to power snatch in 2 days: thinks he is an olympic champion
Learns how to box squat: Now an elite powerlifter
Throws some tires lift an atlas stone: Strongman
Here's my advice if you must do crossfit:
Avoid oly lifts or other big compound lifts if you are tired (mentally and physically). There are much better ways you can achieve your goals without having to resort to crossfit. No one cares that you did 100 reps of sloppy cleans after your swinging pull ups.
Friends don't let friends do crossfit, remember that..