Tiger Woods -- PEACEFUL THREESOME ... Ex-Wife Hangs with New GF

It's shocking enough to see Tiger Woods hanging out with his ex-wife Elin Nordegren again ... but even MORE SHOCKING to see them together with Tiger's GF Lindsey Vonn by his side.

But that's exactly what happened at a tee ball game in Florida this past weekend -- where Tiger and Elin came together to support their son Charlie, who was playing with the 5 & 6-year-olds.

The threesome sat together in the stands -- and while Tiger placed himself between Lindsey and Elin, we're told they all appeared civil ... even friendly at times.