I think my favorite MitM moment was one of the cold opens where Hal comes in the front door, Malcolm and Reece are up against the wall, on their knees, with their hands behind their heads and their noses to the wall, and all Hall asks is how long they're in for and just walk away not listening or caring, like it's totally normal (which, in that house, it totally is).
That or when Hal bursts into the boys' room and offers one of them 50 bucks to take the rap for something he did, no questions asked and you can hear Lois in the background yelling "oh my God!".