Hmm..well for me up until recently I was pretty close to being atheist..not really like that but apathetic towards god etc... i always questioned the truth of the ramayan and if it actually happened etc..
well i guess in that case, those atheist seem to be unsettled by their own thoughts which is why they would question others... this is the only reason to their actions I can think of :S
I feel if one is insecure about what they posess they start to point fingers and try to find the bad in what others have... like I dont know but I never question an atheist why they are the way they are..and thats because I respect their views and I have my own...if we were to get into a discussion about religion..i would not expect them to agree about anything that i say and at the same time i they snever say something to offend them.. but if they start to say stuff like that then its obvious they do not have respect for not only the other person's views but for themselves as well for conducting themselves in such a bad manner.
People can ask many questions as they can and they can speculate as much as they want but at the end its up to your own heart and soul to believe what you want to believe and if your bhakti is true no amount of power/questions/force will be able to shake your foundation... hence the ppl who ask questions rudely to others already seem to have a crumbling foundation..
So noww I know what to do the next time I face such people. Copy pasted and saved Jhanvi's answer in my notepad and also in my brain. Next time if I meet a rude atheist, I ll be ready with this answer :D