fifth wheel

US /ˌfɪfθ ˈwiːl/
UK /ˌfɪfθ ˈwiːl/
"fifth wheel" picture
1.

お邪魔虫, 余計な人

a person who is in a situation where they are not needed or are superfluous

:
I felt like a fifth wheel on their romantic dinner.
彼らのロマンチックなディナーで、私はお邪魔虫のように感じた。
When they started talking about their inside jokes, I knew I was the fifth wheel.
彼らが内輪のジョークを話し始めたとき、私は自分がお邪魔虫だとわかった。