a big deal
1. Something that is considered important or consequential. Being the first in her family to graduate college was a big deal to Katie. I'm kind of a big deal here, but I'll just be the new kid when I switch schools.
2. Who cares? That's not impressive or important. So you did 20 push-ups. Big deal, I can do 100. A: "Wow, a 1969 Mustang!" B: "Big deal. It's just a car."