Conor McGregor Celebrates 36th Birthday W/ Photo of Bulge!

Conor McGregor did it REALLY big for his birthday -- the UFC superstar stripped down to his undies and put it ALL on display ... leaving very little to the imagination in the process.

Mystic Mac went to Instagram to celebrate his 36th trip around the sun on Sunday ... flexing his muscles in his orange Versace briefs while aboard a luxurious boat.

Just like many social posts in the past, Conor's bulge made a special appearance ... something his followers made sure to point out in the comment section.

"Those briefs are fighting for their life," one fan joked.

These types of risqué photos have become quite the trend for Conor ... as he clearly enjoys posting the images for all to enjoy.

Based on the hashtag in the caption, Conor spent the big day out on the waters of Ibiza ... an apparent quick break from the gym as he gets back to training for his UFC return after breaking his pinky toe a few weeks ago.

Speaking of, Conor seemingly hinted it is once again all systems go with Michael Chandler. After the two sides bonded over wishing former President Donald Trump well following his assassination attempt, Conor told his future opponent, "I talked to [UFC president] Dana [White] today about our new date, all looking good! 24' for sure."