Ammonia is an excellent cleaner in the bathroom, it used to be easy to buy it but last time I tried I had some difficulty getting hold of some, if any of our readers know of a good way to get it in their country please let us know. Given a few days to work, cooking oil will combine with the glue and soften it. After peeling off the label, the oily residue responds to hot water and detergent. I have found that if you put peanut butter, preferably not chunky, on glass, bottles, or even mirrors, it will remove the residue. Sometimes it takes more than one application.
Most people have peanut butter on hand.
I use WD40 to remove sticky labels. Just spray a little WD40 on the label and leave it for a few minutes. If the label on the plastic has been wet, or the article has been stored where it was hot or humid, it will be more difficult to remove. Dip cotton end in dry cleaning fluid. Allow the fluid to remain on the label only long enough to allow the label to be rubbed off.