Party Etiquette

My older sister was having a party a few weeks ago, and I didn't know like 95% of the people that were there -which is actually quite typical of my sister, she's the kind of person who can go anywhere, and meet a new best friend before she's out of the parking lot; and this happens probably several times a week- But they're cool, so it doesn't matter.

So I was there with a friend, when we were ready to leave we said good bye to everyone, and my sister, and some people walked us to the door. I thought everything had gone quite well at this party: when I went pee I triple checked that my skirt wasn't tucked in my underwear, I had nothing hanging out of my nose, etc. When I went to leave my friend was still talking to someone, so I was standing there with a group of people I had already said bye to, which is pretty awkward in itself.

My friend finally came to the door, and I turned to my sister's friend, and said "It was nice meeting you-", and I'm still not entirely sure what happened, but for some reason my salivary glands decided to kick in full tilt, and a huge wad of spit came out of my mouth, with great force, and landed on the face of my sister's friend. Everyone burst out laughing (except the girl I spit on); I had no idea what I could possibly say at this point to remedy the situation. I quickly ran to get her a napkin, and I sort of awkwardly laughed and said, "Well I hope you already have Hepatitis!", and made my exit.