It was a card game that used a non-standard deck. He says it had a fairly short name - it seemed like he was thinking it was a one syllable name, so I'm guessing it was definitely a one word name, possibly just one syllable. He says the card themselves were along the lines of items or actions. I thought perhaps he was referring to Munchkin, but he says that wasn't it. He also doesn't think there were any character cards, so I guess that would also rule it out, but I do think it sounds somewhat similar to Munchkin.
One of his friends owned the game, so it definitely wasn't a collectible card game where each player is building their own deck.
Any guesses? He liked it a lot and would love to figure out what it is, but unfortunately can't remember any specific details so we can't really Google it.
Edit: Nothing with numbered cards, guys - the cards represented items or something along those lines. Some cards would do something good for you, some would do something bad to an opponent. Some cards were one-time use things, others had more lasting effects.
Edit again: SOLVED! It was Fluxx!