As a yoga teacher I hate to admit that there are asanas (poses) that are not my favorite. This is especially hard when teaching because I find myself eliminating those poses from my classes. I'm not proud of it. I have various reasons for the omission. Some asanas hurt me. Some asanas are just flat out hard to teach. In some asanas, I'm afraid students will move too fast, or throw their heads back, or just hurt themselves in some way. Some asanas, such as shirshasana (headstand), are just impossible to teach for lack of wall space, props, etc.
Today I taught an asana that makes me cringe with apprehension: parivrtta janu shirshasana or revolved head to knee pose. For me personally, this is such a difficult pose. I'm always anxious about doing it correctly and by correctly, I mean safely. The very last thing I want to do is hurt my students, or myself for that matter. Since I am afraid of this asana, I haven't practiced it myself in months. This does not help the situation.
The way I practice yoga and the view I have of the practice is that there is no absolute in asana. Everyone can do the poses and the poses are unique to each individual. Just because you can't bend yourself into a pretzel doesn't mean that you aren't realizing a pose or that you aren't doing yoga. I use goals as approximations to coax my students deeper into their exploration of an asana, not as an absolute that the student must master.
With that said I find myself eliminating these asanas from my practice because I can't do them! So, in an honest effort to better serve my students and my own practice, I am slowly beginning to incorporate these poses. My bugger of a pose may be bliss for another.
Here is parivrtta janu shirshasana. Enjoy! 

1. Begin sitting with the legs in a wide straddle. Fold the left foot in to rest against the inner right
thigh. Activate the legs.
2. Drawing the navel in, exhale and twist to the left, facing away from the extended leg.
3. Inhale and extend the left arm up over the shoulder, with the palm facing inward. Exhale and
side bend to the right, continuing to twist and open the torso.
4. Lower the right elbow to the floor along the inside of the right leg.
5. Inhale and extend through the spine. Exhale and lower further into the pose. Grasp the right
toe with the left hand. Gently rotate through the ribs to lift the sternum.
6. Exhale and release the hands from the foot. Inhale and raise the shoulders. Exhale and release
the legs back into Easy Sitting Pose.
7. Repeat on the other side.