Something that one puts a lot of time, effort and/or money into and which turns out to be a huge failure. From the first season of American Inventor.
Hey man, I've just spent the last 20 years and all the money I've made in that time on this game that you play with your elbows. It's gonna be huge!!!

Actually, dude, it sounds like Bulletball...
by Cave Troll May 19, 2006
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Peter: Hey Joe, here comes bulletballs Quagmire!
Joe: Hey bulletballs!
by Sonic the head chalk April 18, 2023
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