I was going to refrain from commenting and was just going to continue to just read everyone's threads. However, it is always good to sometimes hear it from the females perspective.
IMO, depending on the mood, how we are being approached with the idea of it entering the back door persay, how much time is taken getting that specific area ready for penetration. Just Lubing it doesn't work, you have to slowly massage the area, make it become a comfortable situation in a not so comfortable area. When we are nice and relaxed, and positioned properly it can feel pretty good.
If you just approach them in a manner of " let me F*** you in the A** and pull out the lube and try to stick it, We are going to freak out, tighten that area, and it will hurt like Hell...
Foreplay is good, prepping all the areas for penetration, get them all hot and bothered to where they want it, and it doesn't matter what hole you put it in... We have 3 of them... LOL