That thin layer of wax-like stuff that can cover every surface in the bathtub or shower after its use. A real pain to get off unless you have some cleaning agents made for it. Clorox and Tilex both make products specifically for soap scum. If you don't want to purchase something new, grab your spray-on oven cleaner. Spray it on, and leave it for the as long as it says on the can. Then you can simply wipe the slime away. Just make sure that the bathroom is well ventilated. Don't have any oven cleaner either? Try toilet bowl cleaner and a rag then. This method will involve more scrubbing, though.