'Shtop' or any word with an added 'sh' sound, stands broadly for an Irish-ism stemming from the colloquial manner in which some natives speak/spoke/will shpeak.
Person A: "We're going out in 'Shligo' tonight".
Person B: "Sounds like a Washte of time"
Person A: Shtop!
Person B: "Sounds like a Washte of time"
Person A: Shtop!
by GetItInTYaSynthia November 23, 2022