A naked fan had the time of his life during the Washington Nationals' rain delay Wednesday -- slipping and sliding all over the wet field -- and pics of the guy's joy ride are INCREDIBLE.
The scene all went down in D.C. ... when shortly after MLB officials paused the Nats' game against the Reds and tarped up the field due to heavy rain -- a dude stripped off his clothes and ran all over the place!!!
For several minutes, the fan -- dong out and butt fully exposed -- sprinted across the diamond and slid on the slippery field covering!!
In an amazing twist -- he ended up INSIDE the tarp roller to escape stadium security ... and video fans shot of him getting in the big tube is laugh out loud funny!!!