The Satanic Temple is a Satanist church based in New York and they've been holding what they call "pink masses," which they claim will make Fred Phelps Jr.’s mother a lesbian the afterlife.
They've done two so far on Phelps' mother's grave and told Vice that they aren't opposed to doing it over the graves of other Phelps family members.
Their website has instructions on how to perform your own pink mass:
Catherine Idalette Johnston is buried in Magnolia Cemetery, Meridian, MS. Other same sex couples are invited to respectfully and tastefully express their mutual affection at Ms. Johnston's gravesite. After a Pink Mass has been performed, every time a same sex couple kisses over the gravesite, the now-gay deceased is said to be pleasured in the afterlife.
It appears as though church members have, also, done a few other things to the gravestone aside from perform masses.