Katy Perry & John Mayer — Valentine’s Day … A Good Day to Die Hard

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John Mayer
 might just be the luckiest guy on the planet — because he spent his Valentine”s Day alone in a dark room with Katy Perry … and more importantly, Katy Perry”s boobs.

J & K celebrated the holiday of love last night by hitting up the historic Vista Theatre in East Hollywood — and the photographer who shot the pics tells us, he didn”t see a soul enter or leave the theater the entire time they were in there … roughly two hours.

The theater wouldn”t comment on whether John and Katy rented the place out for their own personal use — but that”s the only logical conclusion. Pretty baller.

A Good Day to Die Hard” is the only movie currently playing at Vista … but it”s unclear if that”s what the couple actually watched … because Katy was spotted leaving the place holding a DVD.

Probably “The Notebook.”