Acronyms dictionary ISTG What does ISTG mean? ISTG is an acronym that means I swear to God. It can be used to convey extreme seriousness, exasperation, or surprise, and is usually used outside of a serious religious context. Examples of ISTG I hate negative energy. #istg @JeiDisback, December, 2017 Females be sneaky on the low #Istg !!! @swagg72027, August, 2015 these people istg. give her space ffs tsbizzlena, Instagram, January, 2018 SEE MORE EXAMPLES Who uses ISTG? Just Added frito pie, walking taco, .5 selfie, pinkwashing, revenge travel Note This is not meant to be a formal definition of ISTG like most terms we define on Dictionary.com, but is rather an informal word summary that hopefully touches upon the key aspects of the meaning and usage of ISTG that will help our users expand their word mastery.