Justin Bieber reached out to Bill Clinton to apologize for desecrating a photo of the ex-prez and yelling, "F**k Bill Clinton."
Hours after TMZ posted the video of Bieber pissing in a restaurant mop bucket, and spraying cleaner on a photo of Bill -- Justin tweeted Clinton ... "thanks for taking the time to talk Mr. President. Your words meant a lot. #greatguy"
According to Extra, Bieber also called Clinton ... who advised Justin to be careful who he hangs out with -- and then accepted his apology.
No word if Bieber apologized to the restaurant, or the janitor, or the kitchen staff ... or his dignity.