I've never had to worry about this for 18s, because I just look old. But what me and my friends used to do for 15s is book the tickets for them online, print them out at the ATMs, get our tickets ripped and just walk in. Because they didn't give a ****. That way, I never got carded. I did this for around 20 different movies before I actually did turn 15. These days, I'm 17 and buy beer to make my movies a bit more fun. Moral of the story? They don't care. It's people who overthink their **** and come up with "tricks" and stuff to get into 15 or 18-rated movies. Just behave normally, do as I say and watch the damn movie.