I am buddhist, granted a VERY non-practicing one
I was Christian for years. I grew up Presbyterian. That lasted me until sometime in High School when I started to question the existence of ANY supreme being, and especially if that being could have a human son. I continued to go to church so as to not raise suspicion with my family. It's strange, but I came out to my family as a homo 6 years before I was comfortable enough to come out as a non-Christian to them.
I have 2 fundamental reasons for not being a Christian. The first flaw is with the religion itself. I don't believe in God (thought I do believe in a 'higher power'), and I certainly don't believe that Jesus Christ was the ACTUAL son of God. I won't argue that he did, in fact, walk the earth.
My second problem with Christianity is the Christians. I am so tired of people picking and choosing parts of the Bible that justify the things they do. I am tired of Christians thinking they're better than everyone, just because a guy martyred himself 2000 years ago. I'm sick of being told "We love everyone, except homos and women who have abortions." I'm sick of the typical Christian mindset that they are right and everyone else is wrong, and needs to be taught the TRUTH and conform. I often quote Gandhi, "I like your Christ. I do not like your Christians. Your Christians are so unlike your Christ."
I in NO way mean to insinuate that ALL Christians are like this. I understand that the examples that I have are of the bad ones, and that there are also shining examples of the good ones out there. It also doesn't help that I live in the Bible Belt.