I was going to say most hated but it's supposed to be an enjoyable and rewarding pastime!
My 2 least favourite are,
Core drilling, this must be like the way women forget childbirth, you attack it with optimism and get reminded that is a messy, noisy, painful job taking hours.
Drawer runners, I don't know about anyone else but I start off with the best of intentions, measuring and marking accurately. Then revert to screw it on about right, see how far off it is then move it.