Parenting Should Require a Course, and a License
Even a well-meaning, kind parent can become so frustrated with a screaming, tantrum-throwing child that he or she runs out of patience. But one of the worst things to do is to scream back at the child or show intense anger--that just compounds the problem. Most of the time, if it's a young, say, two-year old toddler who is "acting out" it is because he or she becomes frustrated at not being able to express himself/herself verbally. Often, it's best to hold the child lovingly but firmly, and reflect his (using the male pronoun for brevity) feelings, and encourage him to "use his words," if he is able to speak a little.
Sometimes, especially if the child has a history of having his way after a tantrum, it's not so simple--he may not respond to the above method, instead expecting the parent to give in as usual. In that case you might have to isolate the child for a little while in his room, say, until he calms down. The idea to express is, that his behavior is 1) not acceptable, and 2) won't get a response from you. Suffice it to say, it ain't easy being a parent...
But if you step outside of yourself and your situation for a minute (or have the benefit of hindsight, as I do), it can be hilarious.
And then, before you know it, the difficult stage is over (you know, the terrible twos, the tumultuous threes, the frenetic fours) and the kid finally turns...5 years old. And plays Chopin, calming everyone down.