Not an expert here, but my own personal wank on the issue of female vs. male masturbation (having slang terms and being able to talk about it comfortably) revolves around the fact that (in modern society) males are supposed to be sexually dominant and take control of their own pleasure. Hence the talk of masturbation and the pride in it. Women, on the other hand, are typically seen as and are supposed to be submissive receivers, and as such as 'not supposed' to pleasure themselves. Which is completely screwed up, IMO, but that's society for you.