[header] How to keep a straight face [title] Take a deep breath. [step] It's impossible to laugh while you're inhaling. If you're afraid you can't keep a straight face, take a deep breath in and let it out slowly. 
Repeat this as many times as you need to until you feel like you don't need to laugh anymore. [substeps] Don't take a huge deep breath with your mouth open-it might be obvious what you're trying to do.