'Haha!' funny or 'I'm enjoying this' funny? I am guessing it's the latter, so here we go:

Thinking up ideas and planning the layout overlap a bit because I'm also thinking up ideas FOR the layout. Making the skeleton is boring but probably also the easiest because all you have to do is take a 4x4 chunk of blocks and draw it all over the place (according to the layout of course). Making the eyecandy can be annoying, depending on the level. In fact, you should try to make the level's layout match with the tileset you're using, but there are so many tilesets that I can't write something for all of them. Putting in events is also boring and very easy because you should've kinda planned the weapons/power-ups beforehand, and once the eyecandy and layout of the level is all finished, it should be easy to see where the pick-ups, springs/etc will go. You can always test the level and move events later but I wouldn't want to change the whole structure of my level just when I'm about to finish. Testing the level by yourself isn't that exciting, but betatesting it with other people can be fun, but only if they are adequately impressed by it (otherwise you'll just have to go back and root out all the bugs, put in more improvements, which is time-consuming).