I stand corrected. Now that you mention it I can remember the scene in question. But it would still be out of question for friends like Huntress and Zinda to have a threesome with anybody, or for Helena to start having one night stands again, or for Dinah of all people to talk about it so openly (Helena and Zinda being two of her closest friends). And it certainly can not be a coincidence that of all the super-heroines Robinson could reference he had to pick two of the stars of the only all-female team book DC had.
If Robinson had ever read BoP (and I presume he had since Lady Blackhawk is not exactly a well-known DC character) he would know that it was OOC - yet he wrote it anyway. Using a whole page in JLA for two middle-aged heroes (chronologically, if no longer physically) to make a sexual joke about two female heroines who can't answer back (since they now no longer have their own title or a long-term writer).
I have no problem with casual sex if the behavior is in character (ala She-Hulk or the way Huntress was written BEFORE Birds of Prey) but when it's not and then to make it a threesome. It smells of some writer's sexual fantasy. It's just tacky.