For this easy achievement, all we need to do is head to Venonin (North of where Ledecestercire is) and we will see a lot of pillars.
You should see 8 altogether (4 bunched up quite close on either side) and a few steps with a ladder going up.
Head up the ladder, shoot the next one down and climb up again.
Here you will see a fat boy capable enough of throwing you off the roof of this pillar.
He has a few attacks, hits the ground, smashes his tubby gut into you, but one of them he grabs and throws you.
To get this achievement, we need to be close enough off the edge of the roof to be able to get him to throw us off, which would be way more than 30m needed and achievement gained!
His attacks dont really hurt that much but still dodge a few anyway to be safe.
Hope this helps!