I think it is rather bad taste to mock anyone - living or dead, rich or poor, wise or foolish. I have done so in the past, but it always left a bad taste in my mouth.
Would you consider it "bad taste" to mock Santa Claus or the Flying Spaghetti Monster? If not, and, as I believe, Jesus (as described by Christians) is no more real than Santa Claus, what's the difference? Note that I am not mocking someone's right to believe whatever they want. Also note that my linking to the above images does not constitute "mocking".
In any case, I would have no problem with Jesus or religion if it were not for the millions of Christians trying to tell me how to live my life, place incompetent politicians in office (who are at their beck-and-call), constantly try to undo the progress we have made with describing the natural world (via science), etc. If they would just leave the rest of us who find their beliefs not good enough, I would leave them alone. However, they have declared war on science and I intend to do everything in my power to see that they do not win!
If Christians are free to tell me that, as an atheist, I shall "spend eternity in a lake of fire while gnashing my teeth", then I feel it appropriate to inform them that I find them and their beliefs downright silly!
Finally, I do not just have a problem with Christianity; I have a problem with _all_ religions and beliefs that do not hold up to testable scrutiny. I just happen to live in a society where Christianity is especially pronounced.
PS: To borrow a line from Richard Dawkins: I did not mock or insult you; I insulted God. If he exists, I should think him capable of defending himself.
(Ricky Gervais! Too funny!)