Walking in the door, flicking one light switch and having instant mood lighting courtesy of multiple side lights, table lamps, floor lamps that all come on simultaneously.
Not finishing saying the life-changing, desperately urgent and important thing you were half way through saying, because you got interrupted once.
But the one that annoys me the most is being sick. Party the being sick because you're shocked about something/sad/distressed? But mostly for the actual poor puke-performing. Endless coughing - why? In reality, real vomit comes from the gut and doesn't really involve coughing at all - heaving and burping - but it's always cough cough spit more coughing spit. Gah