When you are crossing the Rubicon, you are passing a point of no return. After you do this thing, there is no way of turning around. The only way left is forward.
There was a battle in Waterloo, in present-day Belgium on June 18th, 1815, which Napoleon lost. If someone has "met their Waterloo", it means they have been defeated or met their death.
If someone has a great and sudden change in their ideas or beliefs, then this is a road to Damascus change, after the conversion of Saint Paul to Christianity while heading to Damascus to persecute Christians.
If you do something remarkable, you set the Thames on fire, though this expression is used in the negative; someone who is dull or undistiguished will never set the Thames on fire.