It?s called being inverted, and yes it can be done, there are even a handful of pics and maybe couple videos that show a up close shot of women with very stiff nipples flicking and rubbing them one presses tip in tip and sinks or inverts the others nipple into her own areolas, it?s an odd and some what ache feeling, as you can imagine the blood flow to nipples is high from arousal and thrill excitement and it is being forced back, so yes the cartoon is exaggerated as far as the drawings size of the nipples but it most CERTAINLY can and does happen, especially in a breast fight and or nipple duel. I have both done it and had it done so I speak from experience, good question by the way
