The atitude of an adult. Contrary to popular belief, adultitude is not measured by the amount of physical possessions one owns, or by the ability to drink alcohol or buy firearms and get a job, rather it is possible to notice a higher index of it that is based on socially learned behaviour and observable cues (i.e. politeness, maturity, responsibility, etc.).
Disclaimer: The creator of this definition was very bored while making this, however, he is recovering from such an insufferable state of mind.
Person: "I have personally reached the point of adultitude. I believe my level of adultitude simply can't be surpassed."
Other pesron: "Well, I HAVE MORE ADULTITUDE THAN YOU EVER WILL!!!!!"
Person: "Oh yeah? Well, MY ADULTITUDE IS WAAAAY BETTER THAN YOURS!!!!!"
Both people proceeded to throw a synchronized tantrum in unison that knows no end...