Seems to me that Mac is always faced with other people's bad misfortune.
He is usually having a great day when suddenly, Penny happens to arrive at his house unnanounced with..yes..you guessed it! Trouble!
Or, Jack of course. Need I say more?
Pete usually begging Mac to take on a "small" favor. Which usually ends up being something BIG.
Even when Mac is on his own, he could be having a great day till his tyre bursts on his Jeep.
And then you get those bad day gas attendants.