big deal [singular] spoken
used to say that you do not think something is as important as someone else thinks it is:
It's just a game. If you lose, big deal.
What's the big deal? It's only a birthday, not the end of the world.
It's no big deal. Everybody forgets things sometimes.
an important or exciting event or situation:
This audition is a big deal for Joey.
to get too excited or upset about something, or make something seem more important than it is:
I know I'm probably making a big deal out of nothing, but I'm worried about you.