How do you hold back laughter?

Yesterday, since I was an EMT-B, I was stationed front desk (since we can recognize when someone needs to go back ASAP). Other days I can do cool shit like start IVs, vitals, and splint.

A patient comes in saying that, verbatim:

"my asshole is sore and my dick feels like it got rug burned"

I successfully held it back, but later, my partner and I burst out laughing after he was roomed. It wasn't the chief complaint that was funny, it genuinely must have been uncomfortable for the patient. It was the way he said it that made me giggle.