Zach Galifianakis -- My 'Hangover' Date's 87 and Not Homeless (Anymore)

Stu: So, uh, are you sure you're qualified to be taking care of that baby?
Alan: What are you talking about? I've found a baby before.
Stu: You found a baby before? Where?
Alan: Coffee Bean.

Zach Galifianakis pulled a similar Alan move in real life -- replace "baby" with "homeless lady" -- and you've got his date to the "Hangover 3" premiere ... who TMZ spoke to right before the big event!

Our photog spotted 87-year-old Elizabeth "Mimi" Haist on Monday in L.A. -- the woman Zach rescued from homelessness two years ago.

The story goes ... Zach became friends with Mimi at Fox Coin Laundry in Santa Monica back in 1994 -- where she would help people fold their clothes ... for tips.

When he found out she'd become homeless a few years ago, he decided to help out ... setting her up in a one bedroom apartment and paying her rent.

Zach also began taking Mimi as his date to his movie premieres -- and walked the red carpet with her at "Hangover 2," "The Campaign" ... and now "Hangover 3."