Stupid Sexy Friend

Sometimes a guy really does want to just be friends with a girl; at least as far as conscious decisions about what he wants go; but he can't get rid of his sexual thoughts about her.

Maybe something about her, whether appearance or personality or whatever else, just seems sexy to him. Perhaps he is just so dirty-minded by his very nature that even without much reason for Fetish Fuel he just has sexual thoughts about her anyway. Whatever the case, the lust conflicts with the friendship, and he would try, often not that easily, to conceal the former.

Gender-inversions are probably going to be rarer, given the stereotypes, and even when they would happen, it wouldn't be as big a deal anyway.

Compare AND contast with I Don't Want to Ruin Our Friendship. The difference lies in the reaction of the character feeling the romantic/sexual feelings (and, in many cases, the former relationship between the two): if they're creeped out by their sudden attraction to the person they had always considered a brother/sister, it's this trope; if they're worried that admitting their feelings to someone with whom they've been Just Friends will cause drama or change a group dynamic, it's I Don't Want to Ruin Our Friendship.

Compare Stupid Sexy Flanders, as it reflects on a similar conflict between the sexual thoughts one has and consciously thinking one shouldn't have such sexual thoughts. (And yes, this is snowcloned from it.)

Truth in Television, of course. After all, it's considered normal to lust after someone you don't know, as opposed to a close friend (that you do know).

Anime and Manga

 * Hiyori from Lucky Star often has to stop herself from imagining romantic scenes between her (female) friends Yutaka and Minami.
 * In Yuri series Sasameki Koto, Tall Dark and Bishoujo Sumika Murasame is stuck being Just Friends with Lipstick Lesbian Ushio Kazama (not this trope), but as the story goes on, we find out that  (this trope).
 * From Touch: Tatsuya: "One day, we became aware that one of the three of us was a girl." Thus began the Childhood Friend Romance Love Triangle. Oh, and a good deal of baseball too.
 * in Infinite Stratos, this is VIRTUALLY Ichika's relationship with all the member of his Unwanted Harem, he is indeed interested in them, ranging from cute (Rin, Laura, Char), fascination of beauty (Cecilia) and outright sexual (Houki, probably Char). Point is: He doesn't want to have a girlfriend yet.
 * Hilariously,, disregarded as girlfriend material because "She's just too good".

Film

 * Billy Crystal's character in When Harry Met Sally epitomizes this trope, and it plays a major part in the plot of the film itself.

Literature

 * A lesbian example of the trope occurs in Killswitch, the third book in the Cassandra Kresnov trilogy by Joel Shepherd. The titular android's bisexual best friend admits to having fallen in love with Cassandra, but the latter is straight and the friend doesn't want to affect their working and non-working relationships.

Live Action TV

 * In Buffy the Vampire Slayer, this was pretty much how Xander felt about Buffy after he got past being outright attracted to her and too inept to say so.
 * On NCIS Los Angeles: It's a quick moment, but it's there. When Kensi is compelled to do a quick change in clothes in the middle of an undercover op, Callen's eyes widen. And he politely looks away.
 * For a brief period Angel's feelings towards Cordelia are this, with him sort of horrified that he does feel something romantic for her when previously they were like family. By the time he gets over it there's other issues preventing them getting together... not that there weren't already.
 * In Community, Jeff and Annie often fall into this territory. They're pretty much the Official Couple by this point, but the age difference and nature of the relationship so far has made them both feel somewhat squicky about the idea of hooking up, despite how much they both seem to want to hook up.

Web Comics

 * All New Issues provides the page image; the image links to the context.

Western Animation

 * Brian for Lois in Family Guy.
 * Linda to Francine in American Dad. What makes this more tragic is Linda is unaware that Francine is bi and doesn't seem to consider lesbian affairs as cheating.