Matt had spent the entire time walking round trying to muffle his giggles at seeing all the men in dresses, the girls weren't really funny but the guys... and especially Mello. He'd had to bit his lip really hard to stop from bursting into unrestrained fits of laughter at seeing his grown-up, best friend in a frilly dress. Then there was the matter of being sneaky with the camera so no one would notice him taking pictures of them, especially not Mello.
Mello probably wouldn't care if he didn't take a picture of him, but he did want to take a picture of him... so being sneaky it was.
"Ummm..." he looked thoughtful a moment, taking the time to grin happily at Vash before going back to making the important decision. "Mint chocolate-chip." he finally decided.