Looking at your past posts, you have a PPL, so should seriously know this stuff! Absolutely unbelievable that you actually have to ask!
If it's purely a friend that is taking you up as a passenger, there is nothing you can log. Some people like to put these flights in their logbook just so they have something to look back on, but it has no purpose for granting or renewing any licence or rating.
If he were an instructor and it was all through a school, perhaps you could log P/UT, if it were a lesson, but then what on earth would he be teaching you?
A single crew aircraft has P1, and that's it. Save the rest until you reach actual multi crew.