This is the 13381st most frequent Swedish word.
ungdomsstreck
A "youthful prank" or "mischievous act by young people."
The term 'ungdomsstreck' is used here to refer to an impulsive act or prank commonly associated with the behavior of youth.
Det var bara ett ungdomsstreck när de målade på väggen.
It was just a youthful prank when they painted on the wall.
In this sentence, 'ungdomsstreck' refers to an act done in one's youth that later might be looked back upon with regret as one matures.
Han ångrade sitt ungdomsstreck när han blev äldre.
He regretted his youthful mischief when he grew older.
Here, 'ungdomsstreck' reflects a lighthearted or innocent prank or act committed in one's younger years, often remembered fondly later.