People who just don't fit in — they're a little strange, or somewhat eccentric — are oddballs. If you're a non-sports fan surrounded by enthusiastic football supporters cheering for the home team, you might feel like an oddball.
The kid who brings her book to an amusement park is an oddball, and so is the guy who pushes his dog around in a baby stroller. This informal word for "weirdo" or "misfit" is good for describing someone whose eccentricities are fairly obvious, like your uncle, the oddball who wears full clown makeup to every family gathering. Oddball was first used in the 1940s, modeled after the earlier screwball, first meaning a wayward baseball pitch and later "eccentric person."