I have to go along with the consensus. I had my first "full dress" colonoscopy the winter of '08-'09 (previous one was just a flex-sig) and it wasn't all that bad.
I got by with the stuff marketed as HalfLytely; had previously advised the supervising doc that I knew how to take enemas, but he insisted otherwise, and, in retrospect, I'm glad he did.
About 18 hours before the event, I went off all solid or dyed food, and as an experiment, tried the notorious "milk and molasses enema" for the first time. Although the M&M was effective in generating a lot of gas, I was still passing some solids after two rinses, one including some glycerine to further stimulate evacuation.
With about 12 hours left, I started the HalfLytely. Although the prescription allowed for two quarts of the stuff, I was passing nothing but clear liquid, discolored yellow by liver bile, after about three 8-ounce glasses. (Chilling the Halflytely does a lot to mediate the taste.) So the enemas got most of the residue, but not all of it. And it is vitally important that the colon be as clean as possible.
When I appeared for the event itself the next morning. I asked the people in charge to waive the sedation in hopes i could drive myself home. This was agreed to, with the firm understanding that I would agree to waive any further control over the process at the first serious discomfort.
As it turned out, I felt very little, except for one or two cramps when the "scope" was eased around the major bends in the colon. The two assistants helped out with gentle pressure from the outside, and it was quite a sight to see that trip (starting with a view of my "anal orifice" from the outside, and ending with one of my appendix from the inside.
Which makes for a pretty unusual "bar bet".