A T-shirt is just more item of clothing in your closet, but it has the potential to be the coolest thing you own. That’s quite a feat, considering it’s probably the least expensive part of your outfit.

But what exactly makes a T-shirt “cool”?

Is it the wearer? James Dean and Marlon Brando certainly looked cool in their T-shirts and jeans in movies like “Rebel without a Cause” and “A Streetcar Named Desire.” Whereas people who appear, say, on the TV show “Cops” are quite the opposite of cool, even though they’re wearing the same shirt.

Is it the attitude? A T-shirt featuring the kids’ character Strawberry Shortcake might be the lamest thing on the block to Susie Q.’s big brother, but for Susie Q. And her friends–well, it’s just the coolest thing ever.

Is it the design? Mindy P. mumbled a half-hearted thanks to her high-school boyfriend when he presented her with a Whitesnake concert T-shirt in 1991–in honor of their first date. It didn’t move from the back of her closet for two decades. Now, when she does trot it out for ‘80s parties, she gets all the attention she can handle over her “cool” shirt.

Is it what it represents? T-shirts given to finishers of the Boston Marathon may seem cooler than those given out during the hometown 5K walk-a-thon. But for the walker that finished first–maybe not.

Ironic T-shirts are all the rage these days. As a matter of fact, they’re sort of the uniform of the iPod-holding, always-texting, slim-jeans-wearing person–also known as a “hipster.”

Hipster T-shirts are cool and usually carry slogans like:

* I Heart Mix Tapes
* Hugs Are Better Than Drugs
* Wisconsin: Come Sniff Our Dairy Air

What do you think makes for a cool t-shirt? What are your ideas for slogan t-shirts?