LOL. I've seen them do it. And pay whatever ungodly amount they charge in the Dome. I'm a flask man, myself.
Beer is way expensive at professional sporting events. $8 for a 12 ounce Coors Light at both Gillette Stadium and The Ballpark at Arlington. Last time I went to a Saints game dome foam in a big cup was $5 but that was a few years ago. Probably $10 now.
In the late 70's, early 80's, hell I'm not sure when, I went to an LSU-Tulane basketball game in the the dome. At halftime I went to the beer concession stand and bought 3 cups of draft beer fom me and my buddies. After I paid for the beer and secured the 3 cups in my hands I turned around to go back to my seat. Ex LSU QB and Baton Rouge mayor Pat Screen was right behind me and when I turned around I bumped into him and knocked him back on his ass. It wasn't a hard hit. Just the timing of it. The best thing about it was that I didn't spill a drop of beer.