(the) odd one out

1. Someone who is excluded from or left out of a group for some reason. Ever since my injury, I've been odd one out when my friends go to play football together. John never really fit in with others. Even in elementary school, he was usually the odd one out. A: "I don't have enough room in my car to take Sara too, but I don't want her to be the odd one out." B: "We can take her with us, that's not a problem."

2. Something or someone that is decidedly or markedly different, atypical, or unusual in comparison to others in a group. My clunky old truck is quite the odd one out next to all my coworkers' flashy new sports cars. You're going to be the odd one out if you go to a dinner party dressed like that! With my bachelor's degree from community college, I am certainly the odd one out at this Ivy League soiree.

odd one (or man) out

1 someone or something that is different to the others. 2 someone who is not able to fit easily or comfortably into a group or society.

the odd man/one ˈout

a person or thing that is different from others or does not fit easily into a group or set: That’s the problem with 13 people in a group. If you need to work in pairs, there’s always an odd one out. ♢ Tom is nearly always the odd man out. He never wants to do what we want to do, or go where we want to go.