When an individual is having sex with more than one person. They are mixing sexual "germs/secretions" from one person to the others in which case they are mixing sauces.
"Bro, I have herpes but I don't know who I got it from?!"
"Dude, you have gotta stop mixing the sauces.."
"I am so not into just her anymore man, I am gonna just mix some sauces."