adj. Cuckoo for crack. Or just cuckoo.
Related terms: Count Crackula, crack-pipe-worthy, crackadocious, crack on one's cornflakes.
Real citation: "Known psycho Heather Mills and her gullible knight, Paul McCartney, take this year's prize for the year's biggest no-duh-divorce, fending off competition from Pam Anderson and Kid Rock by virtue of having been married for more than 35 seconds and from Whitney Houston and Bobby Brown by virtue of not being crack-challenged."
(Rebecca Traister, "So long, sugar tits!," Dec. 31, 2006, http://salon.com/mwt/feature/2006/12/31/2006_sex/)
Made-up citation: "My dog likes to writhe around like a furry, crack-challenged loonball. It is amusing."