Many people who have never tried it, think of anal penetration as painful, humiliating, and possibly dangerous. Anal sex is a deal-breaker for many women, and countless men think of anal penetration of any kind as something only gay men do. Despite all the taboos around anal stimulation, how many men have incredible orgasms if their partners put a finger or two up their asses at the crucial moment?
In human anatomy, the same nerves that supply sexual pleasure, branch out and are richly supplied all around the anus (asshole). Anal penetration can be equally sexually enjoyable to both sexes.
If you have read this far, you probably are at least willing to consider stimulating this area on yourself or on your partner. It's true that for most of us, accepting anal penetration isn't "natural", that is, we don't instinctively know how to make it feel good.
On top of this, we have spent a lifetime believing that our bodily fluids and solids are "dirty" and bad. Many assume the asshole is dirty and filled with excrement. It's true that people who don't practice good anal hygiene might have some poop between their cheeks, but the anus itself is self-cleaning and rarely has any fecal material in it. A good preparation for any anal entertainment is to be sure that the anal area is freshly washed (toilet paper alone is not enough in many cases).
Blame it on toilet training
Think for a moment about how we were trained to use the potty. We learned that if we relaxed our anal sphincter muscles, that we would have an "accident". We learned to associate relaxing with defecating.
Try a little experiment. Be sure that you don't have to defecate (not a bad idea to do this soon after you have pooped). Now clean up back there with some warm water. Relax. Put a finger against your asshole. Tight, isn't it? Now, "bear down" gently like you would if you wanted to poop. It won't be easy at first since most of us are sure that something will come out if we do. Don't worry, it won't. Notice what happens to your asshole. It relaxes a bit. That bearing-down sensation is partly the result of anal relaxation. There is a point short of bearing down where you just let your anal muscles go. They stay closed anyway. It's how we are built. Learn to find that point and practice being that way. It's actually healthy to do this all the time.