Justin Bieber & Pal -- Double-Team Topless Stripper ... Ain't No Fun, If the Homies Can't Have None

Say this for Justin Bieber ... at least he shares ... even when it comes to strippers' boobs -- as seen in this photo of Justin and his pal Khalil Sharieff sucking on one breast each during a recent party.

According to sources with direct knowledge ... the stripper, who came fully-loaded with giant fake breasts and a classy rainbow-colored Playboy tattoo, was hired to "perform" for Justin and his pals during a party at an L.A. recording studio.

During the festivities, Justin and Khalil decided to get a taste of the action ... at the same time ... with Justin taking a love-bite out of the left mammary for good measure.

Sources at the party say the stripper looked old enough to be Justin's mother ... maybe that explains the urge to breast-feed.