2. Dropping your weights on the ground
What do you think this is – your basement? Dropping the weights is a wuss thing to do. You either have control of the weights or you do not. If they are that heavy, lift less. Exceptions are for those doing max weights, but even this should be a rare occurrence. The last thing you want to do is have a pair of dumbbells land on your toes or someone else’s and damage the floor.