Conor McGregor -- Crashes Fan's Apartment ... 'You're the F**king Man!' (VIDEO)

Conor McGregor rolled into a megafan's L.A. apartment this week -- after seeing a cardboard cutout of himself on the guy's balcony ... and the fan was so blown away, he could barely hold himself together.

Conor was driving to the gym when he noticed the cutout (which was displayed along with an Irish flag) -- and screamed up to the guy that he would drop in.

What ensues is pretty awesome ... you gotta watch the clip.

As for Conor's opponent at UFC 196 (which goes down March 5th in Vegas) -- we also got video of Nate Diaz in a recent training session ... acknowledging that he might get "merked."

It's pretty revealing footage ... Diaz knows McGregor is a dangerous guy -- but warns Conor not to underestimate him.

One last thing ... check out this video of McGregor hitting up Rodeo Drive in Bev Hills after tooling around in his Lambo -- dude LOVES to be rich!!!

Watch UFC 196 – McGregor vs. Diaz – Live on PPV on Saturday, March 5.