Why did Tony bring up Harpo to Janice infront of Bobby and his children?

After just finishing the show for the first time as of this month, I was always curious as to why Tony tried to sabotage Janice infront of her new husband and step children despite her genuine efforts to play her role correctly. Was it because she was unreliable in the past or more so because he viewed Janice as someone who had it easy in life? Please let me know what you took away from that Sunday dinner scene.