“A neoconservative is a liberal who has been mugged by reality” has been credited to Irving Kristol‘s writing from 1983.  “A libertarian is a conservative who’s been busted” is a jocular one-line saying that appears (always uncredited) in many lists of libertarian jokes.

“A liberal is a conservative who’s just been arrested” was cited in print in 1994; “A Libertarian is a Republican who’s been busted for tax evasion” was cited in 1996. “A Libertarian is a Republican who’s been arrested” was cited in print in 1999 and “A libertarian is a conservative who’s been busted” was cited in 2004.


Libertapedia: Libertarian Jokes
Quips
A libertarian is a conservative who’s been busted.
A libertarian is a liberal who learned economics.

Google Groups: alt.quotations
E. Elizabeth Bartley
2/24/94
(...)
>A conservative is someone who’s been mugged.
>A liberal is someone who’s been arrested.

Yes.

An old political line runs, “A conservative is a liberal who’s just been mugged.”

Thomas Wolfe’s (of _The Bonfire of the Vanities_) recent rejoiner was:
“A liberal is a conservative who’s just been arrested.”

Google Groups: chi.general
Scott Buckner
6/28/96
(...)
>A Republican is a Democrat who’s been mugged.
>A Libertarian is a Republican who’s been busted for tax evasion

Google Groups: alt.mens-rights
Benjamin T. Moore, Jr.
7/24/99
(...)
You know what the difference is between a Republican and a Libertarian is? A Libertarian is a Republican who’s been arrested.

Google Groups: alt.quotations
Nathanael Thompson
10/28/01
(...)
>A conservative is a liberal who got mugged the night before.
>~Frank Rizzo
“A libertarian is a conservative who got mugged by his government."--[?]

2nd Light Forums
Libertarian humor
Bamboo
07/14/2004 07:44 AM
Her are some more:
A libertarian is a conservative who’s been busted.
A libertarian is a liberal who learned economics.

Google Groups: sdnet.general
ICE9
1/29/05
A libertarian is a conservative who’s been busted.
A libertarian is a liberal who learned economics.

connexions
John 08.28.05 at 8:22 pm
A libertarian is a conservative who’s been busted.

Democratic Underground
kittykatkoffeekup
Sun Feb-12-06 03:13 AM
4. A libertarian is a conservative who’s been busted. n/t

Bacon’s Rebellion
Looking for Libertarian Jokes?
Posted on June 9, 2012 by Peter Galuszka
(...)
What is a Libertarian? A Republican who has been busted.