Term of endearment for bus driver Ralph Kramden (Jackie Gleason) given to him by his wife, Alice (Audrey Meadows) when they were first married on THE HONEYMOONERS/CBS/1955-56.
When Ralph told his best friend, Ed Norton (Art Carney) about his pet name “Buttercup,” Norton remarked “She used to call you little old Buttercup? Ha! Ha! You used to be a little cup of butter, now you’re a tub of lard!”
See also – “Bunny“