Crack==craic would be the standard interpretation in AUS.
I’d accept crack cocaine as a stupid riff on the “liberty bell / come for the craic” joke.
It looks like it’s a standard t-shirt design now, so too late to ask the original designer what they had in mind.
If you’re really interested, you could call somebody like rocketdesign and ask them who they thought the original designer was.
Of course the original bell was made in England. When that cracked (probably dropped by the dockers) it was recast. Then the recast bell cracked so they gave up.
But notice how the pun is spelled. Usually the more unusual spelling is the one used in the pun. If there was a joke about craic, I would expect it to say “Come for the craic.”
Bumped.
Some of my recent favorites:
I will wear black until they make a darker color.
What if there were no hypothetical questions?
I’d be more interested if you were more interesting.
I can explain it to you, but I can’t *understand *it for you.
Things just haven’t been the same since that house fell on my sister.
Surely not *everyone *was Kung Fu fighting.
It was me. I let the dogs out.
I’m big in Japan. [with picture of Godzilla]
The NSA has read this shirt. (No, we haven’t. - NSA)
I’m trying to be independent but no one will help me.
My wife says there are two things wrong with me. I don’t listen to her, and… I forget the other thing.
There are three kinds of people in the world: those who understand math, and those who don’t.
Autocorrect can go straight to He’ll
Science doesn’t care what you believe.
Statistics means never having to say you’re certain.
With enough thrust, pigs fly just fine.
PLAN
AHEA
D
If you see me talking to myself, I’m just getting expert advice.
Diagonally parked in a parallel universe.
Living on Earth is expensive, but it *does *include a free trip around the Sun.
When I was a kid we had NINE planets.
I might look stationary, but I’m actually traveling at 733 mph!
Bacteria - it’s the only culture some people have.
I may look lazy, but on a molecular level I’m quite busy.
Bigfoot saw me, but no one believes him.
I’ve had my coffee. It’s safe to come out now.
In dog beers I’ve only had one.
I’m not the droid you’re looking for.
RETIRED. This is as dressed up as I get.
Sarcasm: just one more service I offer.
I think I’ll procrastinate… tomorrow.
Fight truth decay.
Let’s eat, Mom.
Let’s eat Mom.
Punctuation saves lives.
My current favorite Tee-shirt says:
I’m Busy.
Doing nothing.
This was the glaring thing that stood out to me from the first mention of “craic” in this thread. The funny would have been showing the Liberty Bell and mentioning it’s craic, if that’s what they were going for.
So I read through every post before making that very post only to have the T make it in the very last one in 2014. Ha ha.
Oh, it’s Funny T-Shirt Day here in ZombieTown?
Current Fave:
I thought I was in a BAD MOOD
but it’s been a few years, so I guess this is just who I am now.
and the classic xkcd snark is timeless:
Maybe if this shirt is witty enough someone will finally love me.
I so desperately want this to be translated into Italian and made for me. But my sister says modifying “tower” with the adjective “upright” is ungrammatical.
Oh, and that t shirt is from the store associated with oglaf(NSFW) so, search for it at your own risk. You shoudn’t be able to get there from my link.
I have a tee-shirt that says: ‘abductee’
I like to wear it to the clinic. Funny, people never say anything about it to me. 
There’s probably a different word that isn’t exactly “upright”. Would “le torri vertical di Pisa” work? (Not that I’m claiming that’s grammatical.)
Bumped.
Some of my recent favorite funny T-shirts:
*To the guy who invented zero: Thanks for nothing
The NSA has read this shirt [No, we haven’t - NSA]
I’m trying to be independent but no one will help me
I’m silently correcting your grammar
I for one like Roman numerals
There are 10 types of people in this world: those who understand binary, and those who don’t
Autocorrect can go straight to He’ll
With enough thrust, pigs fly just fine
Living on Earth is expensive, but it does include a free trip around the Sun
Diagonally parked in a parallel universe
I may look lazy, but on a molecular level I’m quite busy
Bigfoot saw me, but no one believes him
Math illiteracy affects 7 out of every 5 people
90% awesome; 15% bad at math
I will wear black until they make a darker color
I’ve had my coffee; it’s safe to come out now
Still waiting for my Hogwarts letter
Surely not everyone was Kung Fu fighting
What if there were no hypothetical questions?
I can explain it for you, but I can’t understand it for you
PLAN
AHEA
D
*
(Well, that was interesting. ^^^)
Got a tee-shirt for Christmas: black longsleeve with tiny white letters on the front that say: be bop a lula.
Science doesn’t care what you believe.
Facts don’t care about your feelings.
Right. No doubt whatsoever. And I say that as someone who grew up and still lives just west of Philly.
It’s a tasteless pun on the drug and the crack in the liberty bell.
I highly doubt that there is any other meaning, not even a secondary one.
A few years ago, the Kansas City Irish Cultural Center had a T-shirt that said, “The Best Craic House in Kansas City”. Mine was too small for me, so I gave it to my granddaughter.
A few weeks ago, she wore it to her middle school. A teacher asked her what it said, and she replied, pronouncing the word as “crack”. The teacher immediately told her she had to put her hoodie over it, or replace the shirt with another shirt if she had one. My granddaughter kept telling her that “craic” was the Irish word for “fun”, but to no avail.
I recall being super confused the first time I heard that Van Morrison song Coney Island.
I found this on Teepublic. I wonder if the person who made it has read this thread.
Note that this version lacks both of the other interpretations that most people associate with this episode of Always Sunny.