double-barrelled snotgun

The mucous-filled nose of someone suffering from a particularly bad cold.

Thinking you have contained the snot missiles from a juicy sneeze only to find one of the slimy slugs found its way between for fingers and having a friend or co-worker tell you some hours later that there is snot on your shirt or tie.

It's when your nose is really stuffy and you simultaneously blow air really hard through each nostril, which might be enough to blast snot from both of them at the same time, projecting a scattered tapestry of snot onto whatever you happened to be aiming you face at. It can also be done unintentionally, such as when you sneeze really hard and manage to cover your mouth but it gets diverted to your nose, spraying particles every which way. Regardless it's pretty disgusting so make sure you use a damn tissue next time or if you don't have one sneeze into your sleeve.