It always bothers me when straight guys claim they "can't tell" if another guy is attractive. It's such an annoying form of overcompensation. (It's also not true; maybe a totally straight guy can't make fine distinctions or have a "type," but he can tell you whether Gilbert Gottfried or Brad Pitt is more attractive.) I didn't ask if he gave you a boner, all you have to do is use your eyes and a completely detached, theoretic sense of attractiveness. It won't make you gay.
Likewise, it's really dumb when guys think they have to react to any image of a naked or sexualized man with fifth-grader-ish squeals of "ewwwww!" Is there some rule that if you aren't aroused by penises you must be disgusted by them? Can't you just go "oh, huh, that's a penis alright" and be unmoved, like you were looking at a picture of a deer or a bulldozer or whatever? That also would not make you gay.
I'm always impressed--maybe unduly, considering that straight women and gay men have to do this constantly--by straight guys who are okay with sexy things that don't fit their orientation. A straight guy who can look at gay porn and be amused rather than act like Dracula encountering a cross is Officially Awesome in my book.
I'm not turned on by (most of) the images of half-naked women that pervade media and advertising, but I don't recoil in eye-shielding disgust from them either. The least men could do, in the rare instances where the tables are turned, is show the same decorum.