Panel 1: We are about to see the stupid decision that puts Mike behind a hot-dog cart feeling like the simpleton he is. This is because when Lawrence tells him to forget about visiting mayhem on Liz because she won't let him in until he apologizes for his tantrum and come over to his house, Mike storms towards a side window and growls "No way!!"
If he had done so, he would have been able to enjoy a summer of staring blankly into space being too stupid to find something to do and grousing about parents who act like he's this big nitwit who has to be told what to do all the time.
Panel 2: What he does instead is pound on the side window and yell that no stupid little butt-brained creep is going to keep him out of his house before doubling down on treating Liz like shit by belloing "ELIZABETH! YOU SCUM!!"
Again, we are reminded that Mike sees himself as the victim here and not as the aggressor he actually is. This, I think, is owing to him not understanding that Liz is a frightened and unhappy little girl and not the sitcom monster he thinks she is because he confuses television with reality. Y'see, Elly killed the fuck out of any imagination he might have otherwise had by shrieking any time he explored the world around him so, since he can't put himself in another person's place, he can only see people as characters on television shows.
Panel 3: Lawrence goes back to saying something futile when he tells him to relax, not let her "baffling behaviour" get to him and act as if he does not care. This is futile because we're reminded that we're watching a bloody Warner Brothers cartoon by the fact that Liz has tossed a paper airplane at Mike.
Panel 4: Mike cannot hear him because he's too busy screaming about the fact that Liz is in his room taunting him. This must mean that the paper airplane was a note that said "Look up, Buttface!!"
This is why there's ugly filler art in "What, Me Pregnant?" that has Liz jeering at us. This is probably because Lindy is incapable of understanding Alsy's refusal to be trod upon by an angry idiot girl in any other way.......
Summary: This is the idiotic thing that triggers Mike's rage: he doesn't like the idea of being told what to do and where to do it despite not having quite enough brain power to figure out what to do with himself most of the time. He also doesn't like being reminded that everyone else sees his living space as not really being 'his' as such.