The longer they stand around talking about this, the more burned the casserole will become. When Jon sprays water on it, it's going to be wet and burned. The boys are still excited to eat this horrible meal. Garfield and Jon are bachelors, but what does that mean? Here they demonstrate belief that the freedoms associated with bachelorhood should be relished, even those that are gross, pitiful, and, in the case of the burnt, soggy casserole, not even pleasurable unto themselves. No one wants to eat this mess because it will taste good, but because there is no one to stop them. That is not charred StarKist you're tasting, it is freedom.
This strip also suggests that perhaps the most vital function of a mate is to prevent us from acting like disgusting animals. And so it is that the thing separating us from the beasts is that human beings are trying to impress someone.