Bent (slang) has added or changed definitions through the years. The earliest recorded printing is 1833:
Greene, "Adventures of Duckworth," II, 176. "He was seldom downright drunk, but was often .... confoundedly bent."

Bringing it more into the present, this from National Lampoon, 1975:
"Hey, everybody, let's all get bent, piss ourselves, and send our shorts to China."

A definition that has persisted is: crooked, larcenous. 1914, "His Kisser shows tha he is bent." (Jackson and Hellyer, "Vocab. 17." Extended to products- Bent booze- adulterated or secretly made.

School kids aren't very imaginative. "Get bent" essentially meant 'go to Hell.'
1969, J. Bouton, "Ball Four," p. 389: In high school [ca, 1955] ""Get bent" was used to put a guy down." Still used in an article in "Playboy, 1971: "Get bent, I said."
It was used in dialogue in "The Simpsons," 1990: "Hi, Bart! Get bent!"

These and many more in J. E. Lighter, "Dictionary of American Slang," vol. 1, pp. 136-137. Also see Oxford English Dictionary.