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1.
When a females nipples potrude out to the point they are visible through her clothing.
Damn son did you see that bicthes tits the were nipped out!
by j-dog October 10, 2003
 
2.
1.) When one's nipples become firm and stick out and become very noticeable even if you are wearing a parka. Usually associated with cold weather.

2.) When one's nipples become so hard that you could practically cut diamonds with them.
It's so cold outside that it may cause me to nip out
by Eric Vincent November 06, 2006