You understand immediately what Mark decided upon. It's a vampire costume. It's a bit cheesy though. It's very old-fashioned, down to the fake plastic symbol with a false red gem and red cape. The sort that was already out-of-date in the 1950's. You snort, though not in a mean manner.
"What sort of vampire costume is this?" you laugh. "Don't tell me there was only this one? I am sure that you can find easily a much more stylish one!"
You wave your arm at the rows and rows of costumes around the both of you.
"That's true," smiles Mark and holding incredibly corny plastic white fangs in his hand. "But I want a costume that's still funny and act like an old-fashioned vampire just for laughs. Show people I'm fun to be around, you know? And I won't have to worry about messing this one up too."
Mark's idea has got a lot of merit, you think. He's smart enough not to take himself too seriously. Perhaps you could do the same. You wish him good luck and tell him you'll see him at the party. You need to find the right disguise for yourself. And maybe being a vampire isn't such a bad idea after all...