Generally refers to a nipple which is slippery. Commonly used in S&M circles to describe a nipple which is difficult to attach objects to.
During our first S&M class, I couldn't clamp a clothespin on my girlfriends butternipples so I clamped it on her earlobe instead.
by butterman March 01, 2012
To apply a half a stick of butter to an old woman or hot slut's nipples during hot sex so it melts on their crusty tits. After having the hot sex with the hot slut or the old woman you lick the butter off.
You gave me the most amazing butter nipples of my life last night but you didnt get all the butter off.
by Grant and Mitchell Nasty November 11, 2006