When your at the lake sitting around the campfiremaking smores with friends. The girl next to you does not like browning her marshmallow slowly so she just burns the heck out of it. This way she is enjoying her burnt smore in a rush type fashion. It is not the perfect smore but a rush-a-smore.
This is a common phrase said by party goers usually all night long. After chugging half a bottle of rum, 7 shots of vodka, and 2 champagne glasses, one yells this out as a testament to the great time they are having. Essentially, they are "rushing" with adrenaline and everything else that is flowing through their body.
"Thomas got thrown out of the club, what a rush!!"
"Jon just ordered 2 extra bottles, what a rush!!"
well,it's like an expression someone speaks it when they are amazed at something (explosion/knock-out/big house on fire,etc).
the example will explain better
go to youtube and write god damn what a rush,the video length is 11 seconds.John Travolta says it there