Nancy fired the first shot by the manner she introduced him.The timing was slightly off, but he saw the hand as he was turning. But, decided not to turn back for the handshake.
Trump was certainly not going to initiate the handshake himself.
"Pelosi dropped the traditional greeting before the start of the address, “Members of Congress, I have the high privilege and distinct honor of presenting to you the president of the United States.” Instead, she simply announced, “Members of Congress, the president of the United States.” It was extremely petty and profoundly inappropriate. Putting aside the fact that this is not her tradition, but that of the House, it is no excuse to note that the president was impeached."
She is the petty bitch. To get respect, you have to give it first.