SuperUser just notified me that I earned the Nice Answer badge and one other badge and suggested I'd visit my profile.
Curious about what the other badge could possibly be, I complied, but only the Nice Answer badge were there.
It took me a few minutes to figure out that I had actually earned the Nice Answer badge twice.
To prevent others from facepalming like I did, I'm suggesting the following:
Show a multiplier i the activity tab when the same badge is earned multiple times in the same instant.
and / or
Change the notification to You have earned the Nice Answer badge twice / thrice / N times.