noun
Wasei-eigo from 'handle keeper'; refers to a person who abstains from alcohol at a social event to drive others home safely.
wasei-eigo (Japanese-coined English), from handle keeper
今夜は私がハンドルキーパーだから、お酒は飲まないよ。
I'm the designated driver tonight, so I won't drink.
忘年会
We always choose a designated driver for the year-end party.