Noun: A nipple. Particularly on a woman however, this term could be used for either sex.
Can often times be sensitive and becomes erect when aroused, similarly to a clitoris.
Plural: titty clittys.
1. I'll get things started by tweaking your titty clitty.
2. Damn girl, you must be cold! I see those titty clittys trying to poke holes in your shirt.