most kills, most gold, most minions, most dmg, no S?!

You need to fall into S rank statistics across players who play that same character in that same role. For instance, if you go 10/1/2 with 190 CS as Riven in top, dealing all the damage in your game and whatnot, if the top 20% of other top lane Riven players average at 20/2/12 with 250 CS, you won't rank as S since you didn't do comparably as well as they did. This is across the entire server you play on, so good luck if you play common champs.

it doesnt compare you to others in the same game i compares you to others playing the same champ in the same role. idk if the compare you to local players or globally tho

I recommend RTFM.