Flying and fighting an H-60 helicopter.
I could make it sing and dance, and if you don't believe me I'll punch you in the pants
Didn't cost me a thing; you guys, on the other hand...
I wouldn't start again today, but would certainly do it all over again. Seriously, I got to the point where I felt and knew exactly what the machine was telling me, an almost sympathetic relationship if that makes any sense.