During wave 5 and 10 the slots will play and a 3 things will show. If it shows a guy with an afro, mr. boogie will spawn, otherwise you'll need to wait for next slot time.
In your hud it will show a little icon with his picture where he is on the map, but you need to be close enough. Now he has a good amount of heath, and cant be hurt during his spin move. But when he is almost dead is turn up time. If you dont land the last shot, and be the one who kills him, you will not get this. I confirm this myself by shooting at him then running away to heal and not getting it when he died.