(Strip Number 5003, Original Publication Date, 15 August 1988)
Panel 1: As he takes a fresh box of hot dog buns over to the campfire, Bob notices Mike sitting by himself feeling low and asks him how come he's not at the campfire. Since Mike doesn't like feeling vulnerable, he clams up and says that he dunno.
Panel 2: When Bob tries luring him into the mix by telling him that they're having fun over there, Mike says that it's okay.
Panel 3: Bob walks off and tells Mike "Suit yourself....we'll miss you."
Panel 4: Since Michael is the same sort of narcissistic, literal-minded and gloomy clod Elly is, he looks on at the happy children having fun watching Lizzie give herself second degree burns without him and comes to the conclusion that since they are not wailing in grief at his absence, nobody there really seems to have missed him yet.
Summary: Martha might be about to teach Michael the manners his parents did not but she could never make his IQ grow. His parents are nincompoops so he's a dimwit in his own right. This means that he can't see that anyone who might remark on his absence would shrug and write him off as a butt-hurt crybaby who can dish out the dirt but sure can't take it.