“What’s the difference between a bassoon and a trampoline?  You take off your shoes to jump on a trampoline” is a musician joke that has been cited in print since at least 1992. It also became a lawyer joke:
 
“What’s the difference between a lawyer and a trampoline?  You take off your shoes to jump on a trampoline.”
 
The lawyer joke has been cited in print since at least 1994 and is of unknown authorship.
 
   
Google Groups: rec.humor
Music Jokes
Perry Tarantine
6/12/92
(...)
What’s the difference between a bassoon and a trampoline?  You take off your shoes to jump on a trampoline.
 
Google Groups: rec.humor
Lawyer Jokes
The Fulcrum Group
4/21/94
What is the difference between a lawyer and a trampoline?
You take off your shoes to jump on a trampoline.
   
Google Groups: rec.humor
Need bad lawyer jokes!!!
Hugh Bothwell
10/25/94
What’s the difference between a lawyer and a trampoline?
You have to take off your shoes to jump on the trampoline.
 
Google News Archive
12 August 2000, New Straits Times (Malaysia), “Look What I Found on the Net: Court Humour and Lawyer Jokes,” pg. 8, col. 3:
What’s the difference between a lawyer and a trampoline? You take off your shoes before you jump on a trampoline.
 
Google Groups: 3do.bad-attitude
Good Lawyers?
Drew Pratt
4/10/02
(...)
What’s the difference between a lawyer and a trampoline?
You take off your shoes to jump on a trampoline!
 
Google Books
The Lawyer’s Joke Book:
There Are Some Things a Rat Just Won’t Do
By John Patrick Dolan and Dale Irvin
Charleston, SC: Advantage Media Group, Inc.
2008
Pg. 27:
What’s the difference between a lawyer and a trampoline?
You take your boots off to jump on a trampoline.
 
Twitter
GET LOLIFIED!
‏@TheLOLWorld
JOKE: What’s the difference between a lawyer and a trampoline?
You take off your shoes to jump on a trampoline! http://ift.tt/1ea7Tvx
11:49 AM - 13 Nov 2014