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Has the nonstop squabble-fest that is Lindsay Lohan and Samantha Ronson's volatile relationship finally imploded? All signs are pointing that way after a drama-packed weekend that found the issues-plagued and increasingly unpredictable starlet banned from a Ronson family party and Sam changing the locks on her house.

OK! magazine reports that the trouble began on Friday night at Bar Marmont, where Sam was performing DJ duties at a shindig celebrating the launch of her fashion designer twin sister Charlotte Ronson's new clothing line for JCPenney.

Lindsay attempted to crash the soiree, but she was "held back at the door by five bouncers," which seems like overkill given her slim-line frame.

Word is, the Ronson family had a strict "No Lohan" policy in place for the event, which was also attended by Sam and Charlotte's remix-happy musician brother, Mark, and their mom, Ann Dexter-Jones.

"She was heartbroken," a mole tells Us Weekly, "but Sam did not want Lindsay entering and causing a scene and ruining Charlotte's night."

LiLo, who got her attention fix a couple of days earlier by surprising "Shhh" tattoo pal Lily Allen onstage (check out her odd appearance here -- she pops up at the 3:42 mark), was apparently aware of her persona non grata status.

"Lindsay knew she was unwanted," snipes an insider, "but came anyway, to no avail."

At least she took the denial in stride. And by stride, we mean the long strides she may have needed to pull a Spider-Man move.

X17 claims the actress-turned-self-tanner entrepreneur tried to scale a wall in a bid to enter the party, which is probably the first time anyone has gone to such efforts to get into a JCPenney-sponsored shindig.

But does Lohan's exile extend to Ronson's Los Angeles digs? On Saturday, shutterbugs spotted a locksmith doing his thing on the front door of her house (Lindsay has reportedly been holed up with mom Dina and little sis Ali).

The thrice-rehabbed actress, who last week denied that she and Sam were over, purportedly reacted to the weekend's events in her typically sensible way -- by ranting on Twitter.

"Being cheated on does wonders to you," reads one of the tweets ostensibly posted by Lindsay (via Perez Hilton), while another, more grammar-deficient one, states, "Look, im doing this publicly because u&ur friends call people win, you broke my heart. now go away. i loved you."

On Monday, Lohan confirmed to E! News that she and Samantha are on the outs, but she left the door open for a reconciliation in the near future.

"We are taking a brief break," she says, "so I can focus on myself."

NEXT: Madonna & Lourdes 'Devastated' by Denial of Mercy