There are two sets of 6 levels to get this achievement.
Levels 1-3 shouldn't pose much of a problem, just press LB to grab them, sprint to the nearest blue arrow, and throw them into it, killing them in an amusing way (jet engines, trampolines, a gong, etc).
Levels 4-6 are a bit tougher, as the fans are very numerous and begin to use baseball bats; even pistols and rifles towards the end of Level 6. Therefore, throw when you have the chance, but a safer method is to use the baseball bats they drop (you must obviously kill one first to obtain it) and just hit them with it as they get near the celeb. You only need to hit each crazed fan ONCE for the money to be added to your total.
$100 for a punch
$250 for a melee weapon hit or a gunshot
$750 for a throw into the environment
$1000 for a throw into a blue-arrowed object
You'd be surprised how quick the money racks up from just getting melee hits, but try and get a few throws in when you can.