Do you ever buy thread because the colours call you?  I am a sucker for jewel colours hence the ball of Anchor  perle #8.  Not a good idea!  I like to use variegated thread occasionally but this is the most variegated of variegated.
Anyway that is an introduction to my TAST exercise on buttonhole.  First I want to show my 
Fly Stitch efforts for week 1.
More variegated thread - sometimes one just has to use it - actually I really like it for the spiral.
Then I tried fly stitch as a pulled thread and was  unhappy with what I got  - so we won't count that.
Moving onto Week 2 and Buttonhole Stitch - I have used this stitch in many applications.
I tried Up and Down Buttonhole - it always seems an odd name for a stitch that looks as though it is in one direction only. I have been roaming through my collection of Edith Johns' books and she suggested using buttonhole as an edging - firstly Up and Down
Here it is sitting on a bag using Italian buttonhole insertion in 2010.
Then I tried Edith's 3 sided stitch edge with buttonhole in the loops - definitely needs more practice 
Now for the fun bit - Edith's Experimental Embroidery has some wonderful buttonhole haloes.  Some time ago I tried my multicoloured thread 
And here is the start of my current effort
I have done a little more to it but no photos.  Also I enjoyed trying  Mary Thomas' Drawn Buttonhole
however they are for another post.