Veronika Khomyn and her 4 gal pals spent the weekend in San Juan for what they dubbed a "birthday trip" ... but it's unclear whose big day they were celebrating. We're just glad they're having fun.

McBae -- whose birthday is reportedly in March -- posted a hot shot from their time on the beach ... which reminds us how lucky the L.A. Rams coach really is.

Khomyn posted about the trip, saying "To have you as my best friends is everything. My stomach still hurts from laughing so much this weekend. Thank you for the best birthday trip."

McVay and Khomyn -- who have been together for years -- got engaged while on a romantic vacation in Italy back in June.

"The man of my dreams, my best friend and the love of my life asked me to marry him...And I said YES!!! to being his McBae forever."

We take it these girls will be a part of the big wedding ... and we're here for it.