I'll be the one to say it, but saying no its very hard to do. Also, riding my cbr from the dealership was one of the hardest but most rewarding things i have done to date. I was scared shitless and almost gave up...but I knew if it was something I wanted I could do it.
"Learn from Everyone, Follow No One" -if
The hardest thing I've had to do was give my dad c.p.r till the ambulance got there, he had had massive heart attack. He passed away on the way to hospital. As a result of what I had to do I suffer with PTSD & panic attacks but its getting better these days as I can now control it pritty well now so that would be one of my proudest things.
Deciding to change my life from mediocre to being a high flyer. Went from a weight of 130kg (286lbs) to 76kg (167lbs), went into politics, 'upgraded' from practical university to theoretical university (the latter is more difficult whereas the former only focuses on practical applications of scientifically found theories) and finally found my old self again. I felt like Theoden in Lord of the Rings (that king of Rohan) - finally I had overcome the evil spell of Obesitas the Worthless and became king! Still proud of it - but it was a hell of a struggle in the beginning and without any of that coaching or surgical operations (like a stomach size reducer); purely the will to get it down and discipline. Might the world end the 22nd, I'd at least die as a skinny bastard.
Also getting married at age 22 in a foreign country with a foreign woman, which many would think was terribly risky and would end in a divorce in a year, while we're still happily married 6 years later. Well, 6 is both long and very short. Let's see in 20 years how we are.
I'm very lucky and didn't have very difficult things to do in my life.