@Jennie_fanfiction here is the answer for your Q
Théroigne de Méricour
The term is found in a 1790 French work, The Whore's Catechisms, attributed the revolutionary figure Théroigne de Méricour, who described a soixante-neuf, or “sixty-nine” in French. English picked up sixty-nine by the 1880s, with its numerical shorthand, 69, familiar by the 1970s. :))