Fromstag +do(“party”), alteration ofstag party.

stagdo (pluralstag dos)

1. (UK) Astag party.
   • 2018,The Telegraph: Duke of Cambridge arrives at the Royal Wedding with Prince Harry‎^[1]:

     The Duke’s ownstag do is reported to have been held on a Devon estate, Hartland Abbey, where he and close friends indulged in drinking, clay pigeon shooting, surfing and games.

• See alsoThesaurus:bachelor party.

• dog sat,dog-sat,dogsat