Fide. Can I adjust pieces during opponents time?

Only the player on the move can adjust the pieces, and only his own.

What they said is true, but I've always adjusted my opponent's pieces (if it's far off the square).

Of course only on my time. But I've never had anyone complain or even give me a funny look. It's usually right after they move and they're still writing it down.

(And to be far off the center is really rare anyway, it's not like I'm doing this in even 5% of my games)

Of course, this "not allowed to adjust the opponent's pieces" thing enables you to play some unscrupulous moves in OTB competition, such as h2 to h4 followed by h4 to h5-and-a-half and then h5-and-a-half to h7... saving a whole tempo in the Pawn race.