>What was the first object slid into your rectum?
I'll dispense with the ubiquitous mom-administered RT's and enemas, and the occasional pediatrician's finger from early life.
Then I discovered Tinkertoy rods, especially the pleasures they gave while jerking it around age 8. (Pro-tip: don't try this at home.)
As for adulthood self-pleasure, think it was actually a make-shift enema made from a pop-top dishwashing detergent bottle (filled only with water of course), followed soon by certain fruits and vegetables selected for their different sensual properties.
And finally I got my first DRE at my inaugural colonic session (in those days the DRE was legal, along with her inserting the probe). Exquisite.