A generalization of a person, scene of people, or event that is essentially lame, a cliche, overrated, worthless, overused, amateurish, self righteous, arrogant, condescending, for simpletons.
Yeypants might be amidst a demonstration, showing off, telling someone what or how to do something with a gleem of excitement, bragging, wearing fancy jeans, boasting or maybe simply strutting their stuff quietly or loudly, but in such obsolescence that it is just yeypants.
random: "Dude you are so yeypants for posting this definition."
me: "No dude I'm not, its a definition, apparently you don't even know what it means."
random: "That is so yeypants who cares."
me: "Could be, but if you use yeypants to much you become yeypants yourself."