The person may:
-Throw a tantrum. Ex: Crossing one's arms and kicking one leg about.
- Make a mean face. Ex: Frowning or Shifty-eyes.
- Make angry sound effects, usually done when a mean face is performed. Ex: Quick grunting, or low growling.
- Giving someone an obvious silent treatment. Ex: When you say 'Omg, where did you go?' Looking in the distance when the person is standing in front of you.
People become a Sassy McNasty when:
- They are being a brat and not getting their way.
- They lose in playful competion such as board games or trivia.
- They run out of comebacks.
Words can be added as a 'suffix' to more personalize the title, but they don't change the definition.
If you were to make fun of someones pants and they were acting like a Sassy McNasty because they didn't have a comeback, you could call them a Sassy McNasty Pants.