Rural Irish colloquialism expressing astonishment, disbelief, or even admiration for any random fact.
Variants include "Beat the Holy man" when in polite company, and "Beat the fuck" when amongst friends.
"Johnny down the road turned his tractor over on the road the other night after drinking 14 pints in the local"
"Beat the Lord Jesus!"
"I went to Africa on holiday, and it was 45C every day there"
"Beat the fuck."