Can someone explain to me why people are even saying this lately? My brother has picked up on it, and I don't really think he understands what a prank is, because he proceeded to punch me or trip me up mid-walk and exclaim 'it's just a prank, bro'.

That is such a nice thing to do, it's lovely. In contrast, I once lost my Pokémon LeafGreen game in Malta and my cousin deleted all her data on her FireRed game and gave it to me instead, which was nice until she blackmailed me to buy her sweets because she 'gave me a game'.