Knuckles found the whole situation utterly hilarious. Amy had spent years chasing after Sonic before she had figured out that his heart was only for chilli dogs, but now, a year after having officially given up of the blue hedgehog, he was trying to win her heart.
The echidna had been forced to excuse himself several times from various different parties over the course of the year, simply because his sides hurt from keeping the laughter in too long, and then they hurt even more when he found some privacy and allowed himself to let go, laughing himself silly. He had rolled around on the floor, kicking and thumping and holding his sides and crying before taking a few deep breaths, wiping the tears from the corners of his eyes, composing himself and heading back in.
What he found most hilarious about the situation was that, not all that long after having given up on Sonic, Knuckles knew that Rouge had approached Amy under the mistletoe at a Christmas party, and they'd been going steady ever since. No one felt like breaking it to Sonic though, they were enjoying the joke far, far too much.