Ugh I hate questions like this too.. I never know what to put..
I guess mine is going from a complete beginner swimmer (ie hating to go under water, refusing to jump in a pool, only managing a few lengths of self taught crawl and breast stroke) to a PADI Divemaster during which I had to not only do 2 swim tests but face fears about going under water, breathing through my mouth and not nose, going deep etc etc
Swim tests - one for PADI open water - 200m swim, and the other for DM, which was a 4 part test - 400m swim, 800m snorkel / fin swim, float/tread water and 100m towing swim - all of which were timed and you got more points for doing it quicker, there was a cut off and I only got 1 point more than the cut off
I love diving but due to financial, location, temperature. health and work contraints I have been unable to do much this last year and in fact have had to drop from DM status to just master scuba diver as I cant afford to 'maintain' DM status (insurance, medical, padi fees in return for not very much - UK DMs are treated like scivies a bit and dont generally get paid for giving up their time)