Originally Posted by
MrHalliday
Years ago I would put 4 1.75L bottles (plastic ones)
of a very good but very inexpensive Tequila
in my checked luggage en route to week-long river trips.
One time... only 3 of the 4 bottles made it.
There was a TSA love letter, but just
the standard form saying the bag had been inspected.
At first I figured somebody just light-fingered one of the bottles.
Later, I learned about the 5L rule,
and guessed/understood the TSA was just doing their job.

And Tequila is over 24% alcohol/ 48 proof, so the 5L rule would apply.
I'm curious whose rule this is (the airlines? TSA? customs?) and the rationale behind it?