adj. This describes a bundle of joy--most likely a politician or other sociopath--who just can't keep a good thumb down.
Real citation: "Minutes later, Lieberman built up his speech to a rhetorical summit, pumping a thumbs-up (Lieberman is the thumbs-uppiest of the candidates) at the crowd and shouting: 'We have an opportunity to make the future better by changing the leadership of this country!'"
(Matt Taibbi, Spanking the Donkey, page 77, 2005)
Made-up citation: "'Thumbs-uppiest' is not the sort of praise one wants to hear lavished on his proctologist."