Originally Posted by johndthompson

easiest way is to leave the retaining nut off and ride around the block a few times until the arm loosens up on its own. Don't go too far, because once it comes loose you'll be walking back home. But this carries the risk of damaging the square taper where the crank mates with the bb spindle (you did say destructive removal was an option, though).

If you want to be sure to remove the crank in usable condition, a "pickle fork" (aka "ball joint separator"), jacobs chuck remover wedges, and gear pullers offer safer, but perhaps more tedious, means of removing the arm.