Can someone help me articulate why this is wrong?

He is clearly wrong about a) there's no evidence at all that people are more likely to lie about rape than any other crime.

B is more subtle - it is not unknown for women to go out on the pull and to have the intention of finding a suitable partner to have sex with that night. It is not unreasonable for a man in a club to guess that that's her plan and approach her accordingly. He would cross the line when you make any insinuation that therefore she can't withdraw or refuse consent, or that her word about whether she did or did not give consent cannot be trusted. He would also cross the line if he implied that "she's out on the pull" => "she's a bad person" especially if he wouldn't make such an implication about a man.

With regards to your first point, I don't think there is any evidence of there being more false accusations of rape than of any other crime so the implication that "lots of women are lying" is factually incorrect and sexist.
The onus on court is for the prosecution to prove that the defendant is guilty as it is for any crime in this country "innocent until proven guilty"
With regards to the second point, assuming that a woman wants sex because of what she is wearing is ridiculous. Using a phrase like "she is well up for it" implies that she wants sex with anyone, it doesn't matter who. And to me the big problem with that attitude is that it is then a much smaller jump to "she wanted it, she didn't say no" etc. It is a slippery slope which almost implies that as rape victims go she is not as "innocent" as some one dressed more conservatively.
Sorry, not particularly articulate but those are my thoughts.