The famous case is at airports. They now prohibit a lot of things, just on the off chance that one liquid might be part of a bomb. Meanwhile, no one else can carry 12 ounce bottles of things like shampoo on board. (Some airports may differ.)
One amusing example: A woman who had Breast Cancer surgery was left with scar tissue, that shows up in different colors in the scanners. So she was dragged to the Pat Down area. Except her particular officer was a bit aggressive, and it felt more like a feel-up. Twist: She is an Alaskan State Senator. OOPS!