What does 'ISTG' mean? "ISTG" stands for "I swear to God," an acronym usually used to express the seriousness of a situation or assure you're not joking when sharing a surprising fact.

It is used the same way as its equivalent, to express indifference, distaste or boredom. Prime Day Deals: Shop sales in tech, home, fashion, ... What does 'OG' mean?