Yikes!
I once got grounded at age 17 for something my sister should have been grounded for. My mom was unaware of sis's drinking issues. She was supposed to be at a church function, I found out she wasn't and where she was so I went and drug her butt outta Lake Michigan where she was swimming quite blasted. Now, this was a bit of a trip...and I had a 10 PM curfew. Because she was "drenched", I had her sneak in another door to change and get to bed, and there was mom at the door waiting for me! (I was responsible to get sis home, ya know. Which I did!) I didn't tell mom of sis's condition and got grounded for a week for being 15 minutes late.
Years later we told mom about the incident while we were both visiting her for the weekend. She turned to my sister (then about 40) and yelled "You're grounded! Go to bed!" And meant it! lol