This one was uttered on the t.v. show The View. The contributor was sitting in a doctor’s office and heard it on the t.v. that was above her head. This is a nice mashup of “slippery slope” (a behavior or action will lead to a worse form of the same behavior or action) and “sliding scale” (a system in which the rate at which something is paid changes as a result of other condition). “Slopes” and “scales” are six letter words starting with s and sound somewhat similar, which I think is the cause of this malaphor. Both phrases also describe something that changes as a result of another action. A big thanks to Vicki Ameel-Kovacs for hearing this one and passing it on. She has the ears of a hawk!