Jessica Alba -- Cakes Up for Spring Break with Chrissy Teigen

Jessica Alba still does spring break like she's 23, and she's got the booty to back it up -- as she proved on a Caribbean beach with Chrissy Teigen.

Jessica, Chrissy and John Legend were frolicking in the water Thursday -- and it's almost like Alba's ass knew it had to do something to stand out with so many celebs in one spot.

Mission accomplished.

Not to be a buzz kill, but Jessica's 3-year-old daughter Haven is in the photo too (pink hat).

Sorry. You may now resume objectifying her mom -- and because we have a deep respect for history ... here's a classic.