The 17th prohibition is that we are forbidden to love the meisis or agree1 with him.
The source of this commandment is G‑d's statement (exalted be He),2 "Do not love him."
In the words of the Sifri, "Since it is written,3 'You must love your neighbor as yourself,' one might imply that you may love even this [meisis]. The verse therefore says,4 "Do not love him."