How do I get my teenager to be nice to me?

I have a great teenager. He’s hard working, fun to be around, nice to his sister, in fact, he’s nice to everyone, except ME. When I sit next to him on the couch, he gets up. The other day, he was helping his sister with her math and I said, “Thank you so much for helping her, that is so sweet of you.” He immediately stopped helping and walked away. How can I get my teenager to be nice to me?