BDG is a french acronym that means : « bandeur
de gadgi » or « bandeur
de gadgo ».
It is used to talk about a person that’s
always ready to f*ck with girls (gadgi) or boys (gadgo), or just a person that is easily horny because of them.
Your
friend sees a very not
sfw fanart of an anime character, and tweets that she’s his sexual
slave and would suck his d*ck for hours : you can answer “bdg”.