Parents, what behavior in your children do you really find annoying?

My son just turned 2 and has been a very well behaved child until just a few days ago. He is pissed off that I changed his sippy cup but I needed to go the cheaper route so now when he sees this new cup he has a meltdown. Growling and whining and eventually throwing it. I then begin to sternly yell at him to pick it up and we do this all over again just without the throwing the next time.