"Resident Evil" on the PS1 or "South Park Rally" (also on PS1). My buddy and i probably spent about 20 minutes on those 2 before taking them back. To this day i still can't understand why "Resident Evil" is so beloved.. (Well, okay, in my older years i can appreciate the cheesiness of the acting.)
"Nintendogs" holds the record for game i returned in the biggest hurry that i purchased.. That's about an hour. It actually caused me to return my entire DS because, at that stage, there weren't many titles out there for the system.
When "Advance Wars DS" came out, though, like a sucker i went back and got another system.