pushing the envelope？

Pushing the envelope means going right to some limit, and then possibly exceeding it.

The phrase comes from pilots where the "flight envelope" refers to the conditions that the plane was designed for (it is a little abstract, but the if the plane is inside its safe conditions, you can picture and envelope). If a plane is to withstand 3 G's of force, and you take it to 3.1 G's, you are pushing the envelope (and risking pushing the plane beyond where it can operate safely).

Outside of avionics, pushing the envelope can mean anytime you are close to, or over, some limits. The limits referred to are often limits of safety or taste. For example, I went to a Halloween party I went to where a gentleman was wearing very little more then a g-string and a strategically placed fire hose. In my opinion this was pushing the envelope on taste.