Bumping into someone at the super market and you're not really sorry and you don't want to say excuse me because that is formal you want to say 'mecu'.
To accuse yourself of wrong doing. Usually added at the end of an accusation. Usually used when accused someone of wrong doing mistakenly, when it was really yourself. (Used in How I Met Your Mother)
"You didn't bring us a wedding gift! Shacuse!"
"I did! I brought you that coffee maker!"
"Mecuse?"
"Youcuse (shacuse)!"