I think it's his uber-relaxed manner.
His "I have ALL the time in the world" attitude.
His "I don't have to set my alarm/listen to my alarm/ be upstairs when advised to be" approach.
This turns MY normally easy-going self into a Psycho - "HURRY UP, THE BUS WILL BE HERE IN 5 MINUTES AND YOU HAVEN'T EATEN YOUR BREAKFAST (that's been sitting there for half an hour) YET!!!" - Mom.
I told you this would happen.
Now where did I put my Valium...