Agreed. Buying condoms is nothing to be embarassed about! If the cashier gets uncomfortable, (1) how do you know, and (2) how is that
your problem? Fuck 'em.
Personally, I'd enjoy buying them that way. It'd be funny to plink this person, but then maybe I'm evil.
In fact, now that I think about it, IIRC the first times I bought the things were from females. They didn't seem to have much of an issue with it. I think that if they did I might have suggested I help them get over what was bothering them.
How? By increasing their familiarity with the things. And with my personal condom-wearing appendage.