This achievement can be obtained almost anytime in the game. First of all, find a corner in a safe area. Geddy musn't be able to fall off. Then, throw him in the said corner. Finally, beat him up (Left click by default) 1000 times. You may want to prepare some music or even a video on your tablet or your phone because this will become quickly repetitive. You should be able to get this achievement in less than 10 minutes.