Storm in a teacup

You use it where you could equally well write "fuss about something unimportant" or "a lot of unnecessary anger and worry about a matter that is not important".

There's a storm in my teacup. Oh no, it's tea.

I am more familiar with the locution "a tempest in a teapot." However, this is an example of how i would use the phrase you alluded to:

"Helen and her friends were angry because the company picnic won't be held at their favorite park. But very few people care about that, it's just a storm in a teacup."