Hi J.,
Okay - here's mean mom advice #12...
If you and I were whining all the time, would we ever imagine anyone would want to be in the same room with us? The way I see it is that it's our job to help our kids figure out how to manage their own behaviors so that they can function well in the world beyond our doorstep. All kids go through these phases - my first was like yours - no terrible twos - it came later. But what I've done with all three of our kids is 1) be consistent and 2) mean what you say and 3) offer them two alternatives - one that sounds terrible and another that sounds appealing.
They can either do "x" and enjoy the following OR they can choose to continue their behavior, in which case, they will be removed from what the rest of the family / group is doing for as long as it takes for them to decide they want to be in the company of others. It's simply not okay to scream, for instance, so that other people have to suffer - so, until they choose not to scream, they can go and subject themselves to that behavior, but not everyone else. Then, if they choose the negative option, remove them to a place where they're safe and solitary - their bed, whatever. It's not a punishment - it's a choice - if they really like screaming, they can do it as long as they want, just not around the rest of the family.
Kids are super smart - if you are CONSISTENT, they have no trouble figuring it out, eventually (and each child is different, of course - some are truly more stubborn and will test you more times - but you can NEVER allow them to squeak through even once, as that will undo your hard work at consistent boundaries and rules and consequences).
Oh - and another terribly mean thing I have been known to do is to move on to something fun with the rest of the family while the one is sitting on a bed hollering - like play a game of Sorry or whatever. You'd be surprised at how 'missing out' can motivate.
h - and the best effect is when you're calm and even - matter-of-fact about the whole thing, even when they're at the peak of their worst behavior - it doesn't give them any emotional junk to feed on from you and things go more easily / faster that way (chances are, when they realize they're missing out, they'll still be in an unappealing mode of behavior but wanting to get out of the emotional corner they've put themselves in so if you're totally calm and say, "we'd love for you to join us - as soon as you're calm and quiet, we'll be more than glad to invite you to join us.").
Last but not least - a funny story - we were in a Bob's Big Boy restaurant when I was a child. One of my cousins was with us and he stood up on his chair at one point and started singing. My mom leaned over and said to him, "I want you to look around this WHOLE restaurant...do you see any other child standing on his chair, singing at the top of his lungs?" And he stopped - looked all around - and responded, "no." And she basically said that's because this is not the place for standing on chairs and singing! He sat down and behaved. I still chuckle at that lovely little story! :-)
Okay - that's what I got. Hope it helps - and I wish you joy and patience in this process that does have an end.
Best,
T. B.