Sometimes it is like Italo_DiscoFever says and its a really uncooth guy.
However, in my experience, sometimes its that the guys simply don't see things the same way as girls and vice versa (hence this wondefull site where we know we are receiving inpersonal answers and tend not to take offence).
For example (and I warn you I give terrible examples O_o):
A girl might ask a guy, what he thinks of this or that. The girl might be secretly nervous and hoping the guy will see how the thing in question effects her and that she's looking for a response in understanding.
The guy will just see a straight forward question put to him, and will respond honestly, on many occasions completely hurting the girl with the reply. This is because the guy is thinking "generally" about the question and the girl is "going somewhere" with the asking.
This also happens in reverse, but usually with things girls take for granted as being "general" which guys do not.
So for example, a guy might ask a girl what she did last night, knowing he had texted her asking her for a date or thinking he asked her for a date (he actually just texted "so, what are you up to") and the girl preceeds to describe a fantastic night out, which the guy feels hurt by because his text was unimportant to her.
So, basicly girls hurt guys and guys hurt girls all the time and 90% of those are through misunderstanding. Occasionally you meet someone miraculas who simply understands you, or someone with such common experiences you both naturally talk along same lines and so hurt less regularly occurs. Also, someone who has lived a "intense" life and has a lot of people experience can be more sensitive and spot these sub texts.
Secondly, when we hurt, we say the truths we have been hiding and not sharing because we love someone. We blurt out the things that have pained us and until that point we have not wished to mention them because we don't want to hurt the person. When we hurt, we feel, why am I hiding this, this person didn't bother not to hurt me? Usually, the other person has been SO bothering not to hurt us, and when we hurt them a flood of hurt happens.