Michael was never more reprehensible than at his boathouse meeting with Tom, Rocco and Neri near the end of II:

TOM: Why did you ask me if something was wrong when I came in?
MICHAEL: I thought you were goin' to tell me that -- you were going to move your family to Vegas -- and that you'd been offered the vice-presidency of the house and hotels there I thought you were goin' to tell me that.
TOM: I turned them down -- do I have to tell you about ever offer I turn down?
MICHAEL: let's do business.
TOM: Alright -- just consider this Mike -- that's all just consider it. Now ROTH and the Rosato's are on the run -- are they worth it? And are they strong -- is it worth it -- I mean you've won -- do you have to wipe everyone out?
MICHAEL: I don't fell I have to wipe everyone out -- just my enemies -- that's all. You gonna come along with me in these things I have to do -- or what. Because if not you can take your wife, your family, and your mistress -- and move 'em all to Las Vegas.
TOM: Why do you hurt me MICHAEL -- I've always been loyal to you -- I mean what is this.
MICHAEL: So -- you're staying?
TOM: Yes, I'm staying. Now what is it that you want me to do?

So: Why did Michael hurt Tom--humiliated him--in front of Rocco and Neri? I’m tempted to say, “because he could,” and it wouldn’t be a wrong answer. But I think Michael, as usual, had additional reasons.

What do you think?

Interesting Question. I think by that point Mike was so paranoid and thought everyone around him had ulterior motives. Just shows how far he came from the young man returning from serving his country and wanting nothing to do with the mob life

If memory serves me correctly, prior to that he had Tom appointed as the head of the family while Michael was away; there was that scene where Michael manipulated Tom by calling him his brother, which he definitely knew Tom always wanted to hear.

Perhaps Rocco or Neri complained to Michael about Tom, or on the other end of the spectrum, perhaps Michael saw Rocco and Neri listen more and more to Tom and he wanted to put him in his place.

Or maybe, as you say TB, because he could. But I always found that scene and their dynamic very interesting as well.

I think that he was bullying Tom in order to extract an unconditional pledge of loyalty from Tom. He needs Tom's support to go ahead with killing Fredo.

In the novel, when Tom is released by Solozzo and returns to the compound, Michael is a bit resentful when he realizes that Tom is closer to Sonny than he could hope to be. Perhaps it's a carryover of that?