a joking pun on 'sumimasen' (rendered as 'sumima-sen'en'); used humorously to mean 'sorry' or when handing 1000 yen.
会計の時に千円札を出して店員に向かって『すみま千円！』と冗談を言った。
At the register I handed over a 1000-yen note and jokingly said to the clerk, 'Sumima-sen'en!'
飲み会で割り勘の端数を払うとき、『すみま千円〜』と笑って出した。
At a drinking party, when paying the odd 1000 yen in the split bill, I laughed and said, 'Sumima-sen'en~' as I handed it over.