No, you're not getting it. Idiot or not, your coach's job means that he, not you nor any of the other guys in this relay nor anyone else on your team, gets to decide what events people run. You're here asking how to get out of running the relay. You can keep nagging your coach to change his mind right until it's time to warm up for the race, that's about it for options, but assuming he doesn't, your options are to run the relay, fake an injury or illness, which will keep you from running the 800, or leave the team and run on your own. Whether your coach is ego driven, a genius, an idiot, has no bearing. There is not one thing any of us here can tell you to try to get you out of the 4 x 8 that will position you to run the 800 at that meet instead. Seriously, did you really think someone would have an answer or do you just want to whine about your coach?