No! = Absolute no-go. He'll definitely push your hand away, and probably won't want you near again anytime soon.
Please don't... = Really uncomfortable. Will tell you to stop and either inch away from you or try to politely move your hand.
Um... = Getting a bit uncomfortable. Might not voice it or do anything big, but will get notably fidgety.
Ok! = The neutral zone. Doesn't mind being touched here.
Go ahead! = Touches here are considered pleasant and welcome.
T-that's really nice... = Favorite spots. You'll get him blushing and stuttering with these if you know how to do it right.
As a side note, pay in mind that due to his backfire, Ruby's sense of touch is somewhat hindered. Lightest touches won't register to him, so he really prefers to see if/where you're touching him. Surprise touches aren't pleasant - he won't like it if, for example, he suddenly finds your hand on his shoulder, even if you're his friend.
Sableye / Pokémon (c) Nintendo
Ruby & art (c) me
original meme (c) The9Tard