"Butterfly” and “butter fly” lead to the obvious joke:
Q: Why did the boy throw butter out the window?
A: He wanted to see the butter fly.
The joke has been cited in print since at least 1953. American comedian Patton Oswalt told the joke multiple times on Twitter on April 1, 2015.
“Why did the man throw a clock out the window?"/"To see time fly” is a similar riddle.
1 February 1953, Leavenworth (KS) Times, “Little Moron Department,” The Junior Times, pg. 18, col. 3:
Why did the little moron throw butter out the window?
Answer: He wanted to see the butterfly.
Vernon Tolbert, II
301 1/2 North Fourth.
30 October 1953, Salina (KS) Journal, “Try These Riddles!” by Billy Ledford, pg. 23, col. 5 (col. 1 answer):
Why did the moron throw butter out the window?
He wanted to see butter fly.
8 July 1961, The Morning Herald (Uniontown, PA), “The Junior Reporter Club,” pg. 19, col. 3:
Why did the man throw butter out of the window? Answer. He wanted to see butterfly.
Google News Archive
12 October 1971, The Free Lance-Star (Fredericksburg, VA), “Fun Time—Riddle Box,” pg. 16, col. 8:
Why did the girl throw butter out the window?
10 September 1972, Sunday Herald Traveler and Sunday Advertiser (Boston, MA), Young Folks Page, pg. ?, col. 2:
Why did the boy throw butter out the window?
Biggest Riddle Book in the World, Part 2
By Joseph Rosenbloom
New York, NY: Sterling Publishing Company, Inc.
Why did the nutty kid throw butter out of the window?
He wanted to see a butterfly.
(1/53) Q: Why did the man* throw* butter* out of the window*? A: He wanted to see* butter fly*!
2:10 AM - 1 Apr 2015
Detroit (MI) News
Trevor Noah: Pity the guy who tries to replace Jon Stewart
Tom Long, The Detroit News
12:18 a.m. EDT April 4, 2015
But, in the modern world, every backlash produces its own backlash. So the comic Patton Oswalt tweeted a purposely lame old joke (Q: Why did the man throw butter out the window? A: He wanted to see butter fly) and then followed that with 53 more tweets apologizing for the many ways the joke might be misconstrued or considered offensive.