Sometimes you just CANT laugh for fear of hurting yourself...

One of the main times for that is during a short stint on the Eliptical machine (aka: that horrible machine). If you listen to comedy whilst running you will laugh, lose momentum and then smack your knee of the front of the darn thing at a hard pace! Ouch, Im going to have a bruise the size of Texas.
If you want to hear some serious funny you need to youtube John Pinette: Chinese Buffet. I laughed so hard I freaking injured myself, If thats not funny...Then I dont know what is ;)