A hybrid of 'Excuse Me' and the Japanese word 'Sumimasen,' which means 'Pardon Me,' it is a term used by wannabe Japanese-English bilinguals who have done something stupid, want to only marginally ask for forgiveness, and rejoice in thinking they sound witty.
An American exiting a crowded train in Tokyo: "Excusememasen!"
Japanese collective spirit: "..sigh.."
Clifton: "Ah, did I spill my beer on you? Excusememasen!"
Rika: "ha.. vely funny..and yes you did.."