They say blood is thicker than water, but how about a water SIGN? It didn’t seem that way last month when Pisces Rihanna took her BFF, Scorpio Katy Perry, on an all-star bachelorette party through Las Vegas. The two pop stars were as thick as thieves, posing for pictures together and even holding hands.

This week, it seems the Barbados-born Pisces is singing a different tune.

While promoting her new album “Loud,” Ri-Ri told BBC’s Radio 1, “I didn't want the generic pop record that Ke$ha or Lady Gaga or Katy Perry would do. Every song was tailored to me.”

Ouch.

Jupiter, the planet of expansion, is touring Pisces from September 9 through January 22, a time when the zodiac’s Fish should all be getting a boost of cosmic confidence. Of course, it IS possible to overdose on that cup of courage when Jupiter is in your sign. Jupiter can make people extra competitive. No one would blame Rihanna for wanting to produce a stellar album, but was it really necessary to put down her fellow pop princesses?

Rihanna isn’t the only Pisces who stuck her Manolo in her mouth recently. LA Ink’s Kat Von D (born March 8) has been publicly declaring her love for Aries Jesse James, before the ink has even dried on his divorce papers. Not exactly a gracious move, considering the reprehensible way Jesse treated Sandra Bullock at the end of their marriage.

So far, there hasn’t been a response from Katy Perry, but we don’t suggest Rihanna get any louder with her disses. Hell hath no fury like a Scorpio scorned, and Katy’s sting could come when Ri-Ri least expects it.