LEGO Batman

Further to the above solution, it will need to be policemen.

Easiest level is the one with Bane and the penguin. Take the police lorry and drive tothe point where all the police run out of the building, keep pressing B. When they have all been thrown, return to the area where you stole the police truck and return to the area with the police come out of the building. They keep respawning making it an easy way to get the achievement (and fill up your stud meter).

Easier method than all of the above. Use any character with Super Strength (I went with Man-Bat) and choose any level in free play. Make sure one of your other free play characters is a policeman. Simply use your 'B' attack as the Super Strength character on the second player (the policeman) 50 times, achievement unlocked. The second player character can take 8 hits before dying, so you will need to kill them 6 times and then do two more 'B' attacks (assuming you have never thrown a policeman before that).

Start the level "Rockin' The Docks" from the villain campaign "Power Crazed Penguin" on free play or story, if you choose free play, make sure to take bane as a playable character (sometimes he will be left out on free play).

Destroy the chain-fence on the right with the Demolition suit or the Penguin Bombers. select Bane and just keep pressing "B" as soon as you're in range of your first policemen. when they're all gone.

Use Bane's superstrength to get rid of the trailer that's in your way. Now jump in the truck and drive until you're in front of a citizen that gets beaten up behind some glass.

Hop out and start "B"-ing the policemen that come running down the stairs, they'll keep re-spawning so don't worry you run out of cops. Keep "B"-ing them until you get the achievement.

i found an easy way to do this without having to repeat or leave an area...do the villian campaign and the level "on the rocks" in chapter 1...I chose the character killer croc since he is one of the characters that has the super strength throw.

from the start of the level you are outside of a factory...just make your way into the factory by finishing the puzzle to open the doors...as soon as your inside make sure to switch your character to killer croc.

as soon as you entered the door there is an icy slope that you can't walk up that has 4 or so police men jump down it...what i did was take out all but 1 of these police men by throwing them off the cliff beside you so that there isn't any extra enemies to shoot at you.

now that you have a single enemy left just keep throwing him at the icy slope and he should keep sliding down it without dying(at least he did for me).

gueule d argile tue 50 policiers =

An easy way to get this is to do green fingers, a villain level, 1-3. Go to free play and have one of your selected characters be mr freeze. The last part of the level you will be pumping some stuff to grow some plants, an infinite amount of cops will spawn down and you can get them there. To do a super strength attack: press B to grab and B again to throw down, you should have this in no time.