A semi-pejorative term for polystyrene plastic figurines and miniature model kits made for tabletop role-playing games and wargame simulations, particularly the popular Games Workshop Warhammer Fantasy and Warhammer 40,000 lines. The "crack" designation applies in that fans of these types of games seem "addicted" to them like a drug, and crave buying, assembling, and painting the models, spending large amounts of money and time in doing so, and anxiously await the latest, most finely-detailed releases.
Also used self-effacingly and endearingly by samesaid fans of these games with a good sense of humor about their "addiction".
"Oh, man, it's the new Leman Russ Demolisher kit, and it comes with all the main cannon variants...sweet, sweet plastic crack!"
"Garth came into the comic shop this afternoon and dropped over $300 on plastic crack. Poor, sad bastard...he must live on soda crackers and peanut butter."