Julianne Hough and her 3 sisters are having a kick ass Mexican vacation -- bikinis, sun, cervezas and ... projectile vomiting off a boat!
The former "Dancing with the Stars" judge and pro is down in Cabo San Lucas on a family girls trip -- Mom's there too -- and they all set sail Tuesday. Looked like a ton of fun at first ... and then las hermanas y madre turned their stomachs inside out.
Unclear if the illness was booze or wave induced, but Julianne comforted everyone by making sure to capture their puking on her iPhone.
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