Are you a space cadet? Be the first to land on the moon with an astronaut fancy dress outfit.
To really do this look justice you have to be willing to go in to deep character. So act as if there is very low gravity at the party, “make” the chips float away as if in zero-g, use the “toilet facilities” within your suit.
You also have to keep in regular touch with Nasa which means lots of asides and big quotes “This is one small step for man but one giant leap for mankind”. This should be said at every opportunity including arriving at the party, getting up for another beer and of course going to the toilet.
A great spin on the spaceman fancy dress idea is to go as a cosmonaut fancy dress. This involves wearing exactly the same space suit but speaking in a Russian accent and drinking vodka.