Heee. The characters on Grey's are entirely capable of having a conversation that consists solely of the word "seriously." As for example:

[explain outlandish thing that has happened]
Meredith: "Seriously."
Izzie: "Seriously?"
Meredith: "Seriously!"

I have much love in my heart for it, because it is entirely similar to having a conversation made up of nothing but the word "dude." Which, you know, is a fun time for all! Also, it is really fun to say "Seriously!" and be understood.