When one has two pussies stacked one atop the other, for easy alternating insertion. Usually done doggystyle, this position is used mostly in FFM (female-female-male) porn.
Did you see Ava Devine and Alica Saint in that new Peter North flick? He stacked their asses up into double decker pussies and fucked them both, man!
A special person, for whom you've great and deep feelings. A pupsie is really cute and often say/does things which confirm this. It's really hard to get mad at a pupsie.
Person 1:Where were you? You told me it would take like 15 minutes.
Person 2: I brushed my teeth, put on my pj's and I annoyed my parents a bit :P
Person 1: You're such a pupsie ;)
Person 2: Yeaa yeaa :D