L.,
Monica is right. First, we all get impatient - probably more often than we would like to admit. Second, a big part of being patient with a toddler is understanding that your child is exploring and learning. He doesn't already know his limitations, what is expected of him, how to work things, etc.
I have also found that I sometimes need to change MY way of doing things and be more prepared. For example, if getting out of the house to go to a play date was a situation where I would typically lose my patience because my son "didn't cooperate" with getting his diaper changed and putting on his clothes, I had to find a way to make that less stressful for each of us. I would lay out the supplies the night before and give 15 EXTRA minutes to get ready for the play date. I would also find a way to make a game out of the process.
If I feel myself losing my patience and a situation is escalating, I put my kids (ages 3 and 1.5) in a safe place (childproof room, crib) and walk away for a few minutes (not so far that I can't monitor them). I might grab a quick snack, sit down and close my eyes, read a page in a book or simply count to ten and regain my composure. Then I go give them each a big hug and a kiss and move on. I apoligize if I need to. I discuss the situation with them if appropriate. Of course, at their ages they don't really have anything to add to the discussion but I am trying to model how to manage emotions, how to communicate with others when you are sad or mad, and how to say "I'm sorry".
If all else fails I repeat these words that I once read on a wall plaque - "God grant me the patience to endure my blessings."
Best of luck to you.
L.