The phrase "tie one on" is an American English idiom that means "to become intoxicated; go on a drinking spree". The precise origin of the phrase is unclear, but there are several theories:

• Derived from the term "hang one on," which refers to the hangover that one hangs onto the morning after drinking.
• In the wild west of the USA, there was a notion that you had to tie up your horse to a post outside a watering hole/saloon, hence the "tie one on" saying.
• An old British saying "Tie a bun on" where "bun" refers to drunkenness. One theory is that the "bun" refers to proving your sobriety by balancing a bun on your head, and if you are drunk, you would tie it on so it wouldnt fall off.

Regardless of its origin, the phrase is commonly used to refer to getting drunk or overindulging in alcoholic drinks.