Such people may be devout practicing Christians. To 'use the Lord's name in vain' is forbidden in the Commandments of the Bible, so to say 'Oh my God' or 'For Christ's sake' would be considered blasphemous by a strict believer. Therefore, such peole may change it to 'Oh my Gosh' or 'For Crivvens sake'. Some change it further because they think that even 'Oh my Gosh' is too like 'Oh my God', so they change it to 'My days', 'My land', 'My life', 'My Giddy Aunt', etc. Same with Jews. A devout Jew wouldn't say 'Jaweh!' (Hebrew name for God) in vain, so may change it to 'Oi Vay' or even 'Oi Oi Oi!'. (Apologies if that seems like stereotyping).