Here is a good example:

Hypomania: "I have so much energy, and I want to do all this fun stuff!!!"

Mania: "I am controlling the entire universe with my thoughts."

This is just an example , everyone is different, but the "line" is when delusions start to manifest and the ego goes into overdrive, totally out of control.

With hypomania, there is still some self-control and rational thinking going on somewhat.

With mania, all bets are off... Anything can happen.