On vacation: friends dozing on the long, white mediterranean beach, getting more tanned by the minute. Geek sitting in the hotel-room writing, pondering, then: suddenly: geek running around in the corridors of the hotel, frantically waving arms, hugging complete strangers etc., all while shouting: "Yesss! Ha-ha-ha, oooh, this is sooo great! This vacation was a grrreeeat idea! The genitive! I've finally, finally got the genitive!"
On the bus, going home after a hard days shopping in town: friends gossiping and making comments about the other passengers, geek running the algorithm of the quicksort through the brain, trying to figure out the logics behind it.
On a hot, sunny, wonderful day, geek suddenly realizing that the last seven hours have been spent reading the latest 4000+ newsmessages just in the favorite subscribed groups, and that there's just not enough hours in a day to be able absorb it all.