I have perfected the office appropriate “Quit your bitchin’” and this is me documenting it:

At any point in time when someone complains to you that you that “[they] can’t handle something”, the correct response if you need them to shut ups is: “Most people feel the same way. That’s normal.”

Then there’s no room for them to drone on about it because you’ve already stated that everyone understands, it’s something everyone has to deal with, and they’re just going to have to get over it. It’s best if you override their speech with this response as quick and swiftly as possible even if this means talking over them.