Arrestarti means "to arrest you." It's an unexpected and intriguing word to find in a pop song, immediately grabbing attention.
In the context of the song, the singer uses it metaphorically, saying, "Vorrei arrestarti, manette addosso" (I'd like to arrest you, handcuffs on). This isn't about actual crime, but rather a playful and intense expression of wanting to keep someone close, to stop time, and prevent them from leaving, highlighting a strong desire and passion.
"Lunedì" is about not wanting a good night to end just because the calendar says it has to. Leo Gassmann and L'ennesimo sing about a couple caught up in each other, ordering one more drink and stretching out a moment that should have wrapped up hours ago.
The title, which means "Monday," is the joke running through the whole song: Monday is usually the least romantic day of the week, but here it becomes an excuse. If you're still together this late, on this day, why not stay a little longer?
The playful "I'd like to arrest you, handcuffs on" line isn't menacing at all - it's flirty, about not wanting to let this person go. The song is really about presence: choosing to enjoy the moment and the person in front of you instead of watching the clock.