You probably remember stories of your high school years of teenagers that sneaked in to see an R-rated or an NC-17-rated movie and then they talked about it to their dumbass friends about how they saw a movie they're not allowed (to a teenager, sneaking in to see a movie that they're not allowed to see may be the most badass thing someone can do). If a grown adult did this, they'd be seen as a lame loser that didn't outgrew their high school years.
If someone is over the age of 18 and they want to watch a mature rated movie then they should just buy their ticket, sit down, and watch the damn movie. Why brag about something clearly made for you? It's not a flex.