Probably more than one, if they are not careful, they could start a prank war to end all prank wars. Vongola style~

Oh, if Yamamoto has his way today is just the start of antics that he is dragging Gokudera along for.

"Shit!" He sees the dynamite and excuse him; he is diving under the water, though pretty sure one just about hit his head in the process. He does not surface until he is what he hopes is far enough away to miss any dynamite coming his way. Still laughing even as he has pissed his friend off, "You said you couldn't get the sand off your back, it was this or me brush it off."

Gokudera would rather be wet and down a pack of smokes than have Yamamoto's hands all over his back, right?