Ross: (arriving at the party) Hey...
Monica: (confused by his costume) What are you supposed to be?
Ross: Remember the Russian satellite Sputnik? Well... I'm a potato... or a "spud"... and these are my antennae? So, "Sputnik" becomes...?
(No one is getting it)
Ross: ..."Spud-nik". "Spudnik!"
Chandler: Wow, I don't have the worst costume anymore.