“Why couldn’t the blonde bob for apples?”/“Her brother was using the toilet.”

Bobbing for apples is usually done in a water bucket, but there’s a popular “dumb blonde” joke:
 
Q: Why couldn’t the blonde bob for apples?
A: Her brother was using the toilet!
 
The joke has been cited in print since at least 1993.
 
   
Wikipedia: Apple bobbing
Apple bobbing, also known as bobbing for apples, is a game often played on Halloween. The game is played by filling a tub or a large basin with water and putting apples in the water. Because apples are less dense than water, they will float at the surface. Players (usually children) then try to catch one with their teeth. Use of arms is not allowed, and often are tied behind the back to prevent cheating.
 
Google Groups: alt.tasteless.jokes
blond jokes
Patrick M Hanna
10/13/93
(...)
why couldnt the blond bob for apples?
her brother was using the toilet!
 
Google Groups: rec.humor
Blonde jokes (hey this is new…)
Robin Fournier
10/3/95
(...)
Q: Why couldn’t the blonde bob for apples?
A: Her brother was using the toilet.
 
Google Groups: soc.culture.iranian
About the Blondes
Pahlevan
10/8/96
(...)
Q:  Why couldn’t the blonde bob for apples?
A:  His sister was using the toilet.
 
Twitter
Clean Jokes
‏@CleanJokes247
#CleanJokes Q: Why couldn’t the blond bob for apples? A: His sister was using the toilet. http://ow.ly/39Ou7m
4:31 AM - 7 Jan 2016