Dude, why would you even want to risk it? And on another note, do you really want to be around these kind of guys when you're trying to grab a slot (STS)? I'm not telling you who you should be friends with and who you shouldn't, but if they're going to be doing this kind of sh*t on a regular basis, you should find another place to hang out.
And as far as the previous conversations, I can say for a fact that I know someone that is very close to my heart that lied about their MJ use in HS and came clean about it in the middle of the AFROTC program. He/she was booted without a second glance. If you're just coming into the program, DO NOT LIE ABOUT IT! When I was contracted into scholarship my freshman year, our NCOs told us that admitting it then would not disqualify us from the program. But saying you didn't at the time, then admitting it later, will most assuredly get you knocked.
That doesn't mean you should start toking up just because they don't piss test you in AFROTC.