Hollywood is a very incestuous place.  And nowhere is that more apparent than on the dating scene.  There are tons of examples of celebrities who've dated their friends' exes.  And for some reason, TAYLOR SWIFT shows up in a lot of them.


Check it out . . .


The most recent example is "Twilight" star Nikki Reed dating "Vampire Diaries" star Ian Somerhalder.  Before they hooked up, Ian was dating co-star Nina Dobrev, who is . . . or at least WAS . . . tight with Nikki.


A few years after John Mayer and Taylor Swift broke up, John ended up in a relationship with her friend Katy Perry.


Taylor was also the first among her friends to hook up with Joe Jonas.  After she got her piece, Demi Lovato sunk her claws in.  And then Ashley Greene took a turn.


Taylor and Selena Gomez both had a run with Taylor Lautner.  And Swift also has one degree of sexual separation from Cara Delevingne.  They both nailed Harry Styles from One Direction.


I guess the lesson learned here is that if you're a young celebrity, Taylor Swift will either FRIEND you or . . . you know, do that OTHER thing that starts with "F".


Moving on from Taylor . . .


Selena Gomez hooked up with Nick Jonas after his relationship with Miley Cyrus broke down.  Issues with Miley may have had something to do with Selena and Nick's breakup.  And it seems like Selena and Miley haven't been that close since.


Heather Locklear and Denise Richards were friends . . . until Heather's marriage to Bon Jovi guitarist Richie Sambora ended and Denise swooped in.


It's a shame that Aaron Carter has fallen off the map . . . because when he was a kid, he was seriously pimpin'.  He was datingHilary Duff and hitting Lindsay Lohan on the side.  And he got THEM to become enemies over it.


Kristen Wiig hooked up with Strokes drummer Fabrizio Moretti after Drew Barrymore got through with him.  Drew later said it made "perfect sense" for them to find each other.


After Kate Hudson and Alex Rodriguez broke up, Cameron Diaz went after him.  Kate reportedly wasn't cool with that.


And finally there's Elizabeth TaylorDebbie Reynolds and Eddie Fisher.  Debbie and Eddie were married, but that didn't matter to Liz, even though she and Debbie were very close.


Elizabeth outright STOLE Eddie from Debbie.  That ended their friendship, but only temporarily.  They reconciled, and remained friends until Taylor died.  (And somehow, we came back full-circle to ANOTHER MAN-EATING "TAYLOR".)