Darts! (Not sure if it qualifies as a "sport") During the heyday of the 80's - 90's pub darts craze, i got seriously hooked. Bought a few sets of darts, had lots of different flights, my own bristle board, etc. i spent hours, days, weeks, months (yes - probably invested a good 8 months in this) in my parent's basement practicing.
I got marginally better, but (like golf) was wildly inconsistent and could never rely on a shot going exactly were i aimed it. Sigh . . .
There's a nice pub a few towns over called the "British Bulldog." they have TONS of dartboards and even have league. I've stayed away....