A hormone found in varying levels in both genders of the human species. Typically, in men, it causes them to send aggressive and or ballsy text messages in an attempt to get a girl to date them. In women, it results in massive text-messaging, and, in rare cases, a textosterone storm, where they send text messages faster than you can read them, much less reply.
Girl #1: Omigod, so, yesterday, I put my phone down on the counter, and when I got back like five seconds later, I had 23 text messages from Jane
Girl #2: Yeah, I know, that girl has way too much textosterone.