I'm referring to the following paragraph:
In chemistry class Scott, Stiles and Allison try to keep Erica and Isaac away from Lydia. Mr. Harris quotes Albert Einstein about the universe and human stupidity both being infinite. He then decides that for the class assignment everyone will switch lab partners at each step. This leads to a game of musical chairs which allows Erica to flirt with Scott (with her hand on his thigh), threaten Allison (with extended claws on her thigh).
If a male person puts his hand on a female's thigh without contemplating the need for consent, it's not flirting but sexual harassment. The same rule applies to a female groping a male's thigh.