As other "posters" have stated, it is probably not a deal breaker. However, you need to disclose it on all of your USAFA application material including DoDMERM. I believe on the USAFA application they will ask questions like when did it happen, how did it happen (being where it is legal isn't a defense), how did you feel about it, etc. Answer honestly. But most importantly, be consistent. If you end up attending a Service Academy or ROTC, you will be asked to disclose all drug use on many forms (like security clearances) so make sure you keep the date and circumstance consistent. Good luck.