Whenever I roll back onto my neck to try and suck myself off, and inevitably fail, I wind up fapping into my own face and getting my face all cummy. Afterward, I don't usually feel grossed out or ashamed of myself (well, except the first couple times). Instead I actually feel even a bit more satisfied than I usually do after fapping. I wonder if this is why.
I notice they didn't do the same study with a group of gay dudes, to see if the effect is gender-neutral.