[late 18C–early 19C] stepping into a heap of excrement.
SE in slang uses
1. [1930s+] of a prostitute, to encounter the first customer of the day.
2. [1960s] in general use, to have a piece of good fortune.
1. [1910s–70s] (US) for a white person to have sex with a black person (esp. for the first time).
2. [1970s+] (US gay) to perform homosexual sex for the first time.
[1910s+] (Aus.) to use up or run out of luck.
see Chinaman’s luck under Chinaman n.
[1940s–60s] (Aus.) a description of any lucky person.
[1930s+] (orig. Aus.) signifying envy, jealousy of the person addressed, i.e. I wish I had ...