How do GMs “play the man, not the board”? How do GMs &quot;play the man, not the board&quot; as some books say? Would that work for club level players or could they use other methods? Prepared variations? Trash talk?
What are the ways one can play the man but not the board that are they legal under FIDE rules and would not be called annoying the opponent or the like?
As you mentioned, playing the man can mean several different things, but before I answer I want to say that no one can become a better player by only playing the man - objectivity is the number 1 priority. 

Many top-level GMs do play the man and the most notable example I can give is the Kasparov-Kramnik match in 2000. Kramnik knew that Kasparov disliked queenless middlegames, so he put the Berlin into his opening arsenal. Kramnik also played d4 in his match because Kasparov was known to be a deadly Najdorf player (it should be noted that Kramnik did play e4 at that time). Another example that I can think of is a younger player taking advantage of an older player's fatigue and grinding the position down for hours. These are the main ways that GMs play the man as far as I know.