Human breast milk to be precise, and your mothers doesnt count! 
Im curious, im BFing at the minute and I don’t know why, but the idea really weirds me out. My DH in his sleep deprived state when baby was a newborn tested the temperature of some expressed milk on the back on his hand and licked it off without thinking. He said it tasted like sugary milk. 🤣
Also there was a show on the other night called breastfeeding my boyfriend which freaked me out even more!