Here is a message that I received recently that I will post here anonymously in order to answer:
"Dear Olivia,
Now that I have been fucked by a strap on, is it weird that although I have no interest in men, I want to feel a shemale´s cock filling my ass with her cum?
I would only want a shemale who really looked feminine. I even have the urge to suck her cock if asked to!!"
Dear Anonymous,
No, it isn't "weird" (no sex acts are weird to Auntie Olivia), but it just sounds like you are feeling experimental. There is nothing wrong with this. Naturally if you're experimental, you're going to enjoy strap-on sex and graduate from there to other experiences.
For the rest of the straight men out there, relax. Strap-on sex is not like a gate-way drug to bathhouses and dwarf orgies!
Think of it this way: just because you smoke marijuana, doesn't mean that you are destined to become a heroin addict, but those people who do end up as heroin addicts have probably tried marijuana at some point early in the game. Similarly, men that want to be with a shemale are probably very open to strap-on sex as a precursor.
Now... let's think of sex as a spectrum of experiences and desires. Everyone has their limitations and their curiosities and it's important to find a balance that you're comfortable with.
There is nothing wrong with being intrigued by or aroused by the idea of a shemale. As pretty as some of them look however, it appears your urge is to experience cock. Sometimes the idea of a shemale feels more comfortable as that gray zone between a woman and a man, and if it's exciting to you, then I encourage you to explore! Don't worry about getting hung up on labels like "what does this mean?" and "am I bisexual?"... Society is so focused on putting us all into neat little boxes, but when it comes to sexuality, my opinion has always been to do what feels natural. A little experimentation doesn't have to mean anything.
Sex is all about exploring desires and what feels good until you hit your limits... sometimes those limits change over time, but it's certainly very normal.
Active Ink Slinger
I'm thinking labels are just stupid so do what ya like! Unfortunately many straight men who love receiving anal sex have a great fear they will be labeled as gay which is not the case at all. 
I almost had a crush on a T-girl at one point in my life. She was an internet model and had alot of boyfriends. I have had a sexual fantasy to have a threesome with a man and woman couple, but a "shemale" is very erotic to me because it is like getting a threesome without having to have a third person. I think a tranny could fulfill my bisexual fantasy all by herself.