what's the meaning of holy beetlejuice?
I am a native US speaker, and have never heard the phrase. I would think that it is something somebody made up.
This may be related, but in the 1960s, Batman came on TV in the USA and other countries. Batman had a sidekick named Robin. Robin's signature was to say "Holy <blank>, Batman". The <blank> would be some random word. It kind of stuck as a cultural phenomenon. Perhaps that is what the person who said "Holy Beetlejuice" was referring to (even if they did not know that is where it came from).
Also, Beetlejuice was a popular movie in the late 1980s in the USA. It centered around a young couple who died, became ghosts and accidentally called another ghost to get rid of the living people who moved into their home. The ghost they called was named "Beetlejuice" and starts causing problems for the young couple ghosts and the family who moved in.