Is a deadheading FA allowed to drink while flying?

i am curious because the flight this morning was so empty everybody got the upgrade and we still had 5 seats empty so an in uniform pilot and out of uniform (but wearing the ID cards) FA took two of the F seats. I just happened to notice her original seat was “FA JUMP SEAT” but during pre departure she asked for two bottle of liquor declaring quote “it was vacation time for her and she was heading to X Caribbean location”

i think the dead heading pilot was a little shocked making the “oh that’s funny joke” but I’m trying to give you a hint

on a different note wouldn’t you just put your work ID in your pocket so nobody would know?

Im not Gladys Kravitz so I’m not saying anything or writing delta about this or anything just more curious if it’s more bad form or against rules?