When did I become such a hypocrite?

What is it about parenting that makes you become a hypocrite. I get so frustrated with myself because of this! Just for one example--this morning, Will was not being easy. Didn't want to get a diaper change, throwing food, his cup, his fork, playing in his food, hitting.....and the list goes on. So I spent most of my time fussing, making him hand me things, putting him in time out and yes, I will admit it, yelling at him. Then Troy and Will were playing and Will wasn't listening to Troy's rules of playing--Troy has to lay down the law you see--so Troy started yelling, fussing, making him try again.....and what did I do? I yelled at Troy for yelling at Will. I fussed at Troy for not understanding that Will is only 17 months old (something I need to remind myself). You can see where I am going with this. Troy was simply copying what he was hearing from me and yet, I got angry with him. This happens a lot unfortunately and it's tough explaining to Troy why it's okay for me and Jay to discipline/fuss and not him. I hear myself in Troy all the time and it makes me sad. He makes me realize just how much I fuss at them when I hear him playing with toys and that's exactly what he's doing--fussing and putting them in time out. He'll even spank them which is strange since I haven't done that in 2 years when I realized it simply didn't help my situation. I can't say that I will stop disciplining them and trying to keep them in line, but I certainly need to stop being a hypocrite when Troy copies me