A "Hot Willis" is a variation of the "Hot Carl". A Hot Carl is when your partner has a piece of saran wrap over their face and you take a shit right onto the saran wrap, the poo warming their face. The Hot Willis variation is performed by pulling away the saran wrap, crapping directly onto their face and then jumping up and yelling "What you talkin' 'bout, Willis?" alah Gary Coleman from Different Strokes.
At my high school reunion, my math teacher wanted me to give her a Hot Carl in the bathroom. So, I followed her into the john, assumed the position and delivered a Hot Willis instead.