Since I'm low tech guy, I couldn't get the t-shirt to post but this is the slogan I was wondering about:

"» Via Derby Skates » Ladies Apparel » tee's » Jam Out With Your Clam Out!!!!

Jam Out With Your Clam Out!!!! "

It just seemed like something that needed some explanation.........
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"I didn't care what she didn't 'low--I would boogie-woogie anyhow" John Lee Hooker