In the Murphys Law 3, the object is to ruin the old mans big day. He's about to be interviewed and your job is to make him come out as bad as possible. Some of the themes are adult, so discretion is advised.
In Murphys Law 4, you're going to ruin the mans haircut and preparation (I think he's a politician).
I'll post walkthroughs in the comments section, so that I don't ruin your experience by giving it all away up here.
Play Murphy's Law 3 at flashgamesite.
Play Murphy's Law 4 at funny-games.
Related: Murphy's Law Walkthrough.