To predict a negative outcome for a team or player that your friend likes but which you despise and has no chance of coming true and is completely childish.
...Dave - Tom Brady is a no talent ass clown and the Pats will not win a game next year.
...Ben - You're just saying that because you hate the guy and the team.
...Dave - And he's going to break his leg.
...Ben - Don't prognostihate on my team, bro!