It would be so much quicker to write a list of the things my 12 year old son does that do NOT annoy me!
But anyroad, here are the annoying bits;
Drink all the juice/milk in the carton apart from the last thimble full so he can put the carton back in the fridge instead of having to rinse it and recycle it
Not put the bread/butter/marg back in the fridge after making a snack
Leaving a trail of breadcrumbs through the house whilst eating the aforementioned snack
Leaving freshly ironed (by me!) clothes piled on his desk / chair for days and days instead of putting them in the wardrobe as requested.
Putting the pile of ironed and unworn but now hopelessly crinkled clothes which have been languishing on the desk / chair for a week back into the wash when asked if he has anything for the laundry.
Scatters school books / homework / equipment through his bedroom and under his bed, forgets it is there and then wonder why he can never turn up to school with the correct books / homework / equipment.
Leave his damp towel on his bed.
Leave his school blazer crumpled in his rucksack and then blames my bad housekeeping skills when form tutor gives him a detention for looking untidy.
Hides sweet and biscuit wrappers under his back and then looks all amazed when I find them and confront him about his eating and tidying habits.
Wears his trousers halfway down his backside to show his neon coloured pants. Apparently it is cool 
Starts every sentence with "Basically"
Is rapidly growing taller than me
Will insist on wearing shorts in winter and thick jeans in summer
Oh gawd, there are so many more. But I am getting cramp in my fingers...
(he is lovely though, really)