Christianity suffers from a number of stereotypes.
Hypocritical - It seems that what some Christians say and what they do are at odds. They claim not to be judgemental while judging others, they claim to be all about love while spreading hate. They talk about sin and how people should stop while living in sin. There are other examples but you get the picture. There is a lack of consistency between what is said and what is done.
Homophobic - Many groups of vocal Christians treat gay people as not worthy of their love or the love of their god. They focus on one aspect of their lives and roundly condemn them as people, often projecting hatred rather than the love they claim to feel.
Judgmental - The Christian stereotype is that they are prideful, self-righteous, and act as if they are better than others. They act as judge and jury toward others, instead of leaving that job up to their god.
Intolerant - Christians have a reputation for having little pateince for discussing differences in values, beliefs or opinions. On forums it is almost a given that outspoken and intolerant Christians will block you long before they consider discussing their beliefs with dissenters.
Too political - Using politics to force their beliefs and morals on other people; limiting other people’s freedom and rights, based on their beliefs. Even though we don’t live in a theocracy, many vocal Christians seek to impose their beliefs on people who don’t share them.
Superficial - Another stereotype for Christians is that they are regarded as not knowing what they believe or why they believe it. They can certainly come across as lacking even a basic understanding of science or of differing points of view.
I'd like to close by saying that these are stereotypes, not an attack on Christians. How valid do you think that they are and what do you think that Christians can and should do about them, if anything? This discussion is about the negative perception of Christianity. Feel free to raise your own stereotypes, both positive and negative if it aids the discussion.
If this works out as a good discussion then we could repeat the exercise with another religion or even atheism.