head over heels; madly in love
Fixed expression often used mockingly or teasingly about someone being overly love-struck. The phrase pairs two verbs meaning 'to fall in love' and 'to be inflamed with passion', emphasizing a state of romantic infatuation.
Those two seem so head over heels that they can't focus on work.
惚れた腫れたは若いうちだけだと思ってたけど、違うみたいね。
I thought being madly in love was only for the young, but apparently not.
A fixed expression combining the past tense of 惚れる (to fall in love) and 腫れる (to swell, here figuratively 'to be inflamed with passion'). The pairing creates a rhythmic, mocking tone. The exact origin is uncertain, but it is a traditional colloquial phrase.