The Huey Back, a combination of leaning left to reach to collective, being bent over a little, but having to tilt the head up to see over the panel, while wearing a helmet, and copping that 1:1 bounce for 2500 hours.
I did manage to scrounge a wedge-shaped kidney pad from a Martin-Baker Departure Lounge, and with a velcro strap to let me move it up and down the seat back, the rest of my Bell career in 206, 407, 212 and 412 were almost acceptable.