Supernatural: Sam has Tourette Syndrome -- preferably without the cursing, but with physical tics and vocalizations. It waxes and wanes depending on a variety of factors -- worse when he's stressed, better (or almost gone) when he's intensely focused. Though he used meds during his time in Stanford, he feels they slow down his reflexes during a hunt. I'd love to see a fic set in early or mid S1, where Sam's going off his meds and dealing with his grief, and Dean isn't sure what to make of this Sam he barely recognizes (and perhaps he wasn't diagnosed until he was at Stanford).