From the perspective of geomantic omen, what effect will it have to engrave the names of friends of the opposite sex on themselves?

This is untenable logic. First, the so-called geomantic omen refers to geography, that is, the home of yin and yang. Secondly, if it does, it will affect your military service and many aspects of your future, because tattoos are considered violent or antisocial in China. Third, it will affect your future family and marriage. Take it easy. If you are impulsive, you will be punished.