I have an opinion on that matter so I'm going to try and share it. I laughed at your joke (though I would personnally have stayed with Jesus because I just can't resist unicorns) and I think I know where you're coming from when you say you are offended that you cannot express freely your disagreement towards religion. I'm a litte bit annoyed, as you seem to be as well, when religious people say things like "Jesus loves you" or "God will help you through this" because, as a die hard atheist, to me it sounds as if they were saying "the night fairies will help you through this" (in fact I would be more inclined to believe in the power of fairies). What is an atheist supposed to respond to that? "Thanks, but... you're delusional" ? We could argue that they should assume other people don't have the same beliefs as they do and therefor they should stop annoying us with their beliefs. However Christianism is a very widespread religion so it is sort of natural that christian people will not assume such a thing (I'm talking about christianism because I think this is mostly the religion that we are talking about here). In the same line of thoughts, it is probably also accurate to assume that there is a fair amount of christian people here and that such a joke will surely offend them.
Now as Nathaniel said, when you say you are offended by people expressing their christian beliefs, it's a little delicate to do anything about it. When they talk about God, they are not trying to offend you, they are just speaking with the words that express the world that they live in, in which they often have been raised. They are not talking "against" unbelievers (I mean not on this forum anyway). When you make a joke about Jesus, it's funny for us atheist, but we all know there is christians here and it's going to make their ears bleed a little, and you choose to say it anyway in all awareness.
That being said, should they disregard your joke as we disregard their speeches about God and Jesus? I don't know the answer to that question, but I think that for the sake of decency, without necessarily censoring ourselves, this is important that we pay attention when someone mention that our words might have been offensive for someone else and take some time to think about it. This is also relevant, I think, that the offended people take some time to reflect on the reasons why they are offended.
Which would lead me to 3 questions (beside the main one): Why are you so offended with christian beliefs (I'm not asking you to tell us, I'm talking about personal introspection), are christians offended by your posts here when you talk against, or make jokes about christianism (for all I know I haven't seen any christian participate to this conversation?), and finally should christian people, knowing that it's a little annoying to atheist, be careful not to throw their God loving at us, especially when they know they are talking to someone who is offended by it?
And one last question, did you start this thread to have this current debate or you were talking about an actual debate about religion (did Jesus exist or not etc.)?
Interesting discussion anyway.
Sorry for the long post.