That is most definitely not a hard rule.
Had a flight a couple weeks ago in F where the FA gave me 3 bottles when I asked for a Woodford and Diet and I was leaving Vegas at night, so you can take a guess as to whether I was completely sober or not lol. I didn't even want that many and slow rolled drinking them, don't even think I finished it all.
On the way there a different crew completely loaded me up too.