הסתפרתי, histaparti: I got my hair cut
One word in Hebrew, five in English. CRAZINESS
This is not a revelatory milat hayom. If you have studied Hebrew for a year, maybe a bit more, you know this word. But I just got my hair cut. It's on my mind.
During the summer between fourth and fifth grade, I had a Hebrew tutor and asked her how to say "I got my hair cut" for the requisite composition (חיבור) I would write about the previous week.
She said histaparti. I was blown away.
It still gets me every time.