someone tell me what did i just say?

today in class i was feeling a little bored, so i just randomly uttered this phrase:

"i've got blood in my stool!"

and everyone near me who heard started cracking up, until our professor asked us what's so funny, and my friend asked me to repeat it to the whole class. when i did, the entire class starting laughing so hard, even my professor was grinning.

he merely continued the lesson after that.

but i don't understand what that phrase means...or at least i don't get what's so funny. those around me wouldn't tell me. is it an american thing?

 

Haha... I think it's really funny if you say it in the middle of a class.

 

a stool is a poo, turd, crap, shit,
not just a chair
you told everyone you have anal bleeding

 

ohh buddy its dishonourable!!! what did you say..
you're just kidding us. its full of shit

 

uh oh, thanks samantha! now i know how i've just embarrassed myself in front of an entire class.

now that i think of it, it was pretty funny! y'know, thank god i didn't know what it was just now, at least it spared me the moment of embarrassment at that time.