I think the mistake a lot of guys make is they have gotten things out of order. Some do it deliberately by "cutting to the chase", which they use as a deliberate strategy to find out immediately where "the girl" is coming from. However, many other guys simply don't know or realize what they are doing in the process. They have not been taught or educated about etiquette and protocol and social graces, and how to be a gentleman, etc. They simply have no couth, and this is born of ignorance! Then, when they get turned down and socially embarrassed, they stand there bewildered, wondering what they did wrong.
Guys who talk about "sex, sex, sex" on a first date or encounter often get that from some back room "talk with the boys". Certain ones begin telling their tales of who and how many girls they have exploited or conquered and gotten away with it- How you gotta take control of the situation, like the caveman- Me Tarzan, you Jane! Grunt! Grunt! They think that by being macho and chauvinistic and dominant (assertive??), the girls will really be attracted to this, and so they use that as their modus operandi. The truth is, very few women find that attractive; on the contrary, it is a complete turn-off.
When it comes to dating, or "hooking up" or "connecting", there are some definite steps that must be followed, if you do not want the potential for a relationship (i.e. down the road), or even just a friendship, to end in failure or termination.
First there are the introductions, where people meet each other. At that stage, they are "sizing one another up", getting and making first impressions about each other, and finding out what each one wants or is looking for. This does not give anyone a "license" to pursue the other person to the next level. It is about exploration and discovery, and finding out if both of you want to pursue things further, OR NOT.
If it turns out that this is merely a "friendship" such as platonic only, then that boundary should be respected (on both sides). One does not have the right to "invade" the other person's "space", or make presumptions about the other person. This often happens if you have been acquaintances along the way, and then suddenly one of you begins to approach the other one at a "friendship" level, which kind of jumps beyond the mere "acquaintance" stage. For example, you wanted someone to accompany you as a "partner" at a wedding, but that's all you wanted. He may have, rightly or wrongly, taken that as a signal that you were interested in him beyond that level. Then rather than explore that with you to find out where you were coming from, he fast forwards another 10 or 15 steps to the "let's have sex together" stage. Here again, he doesn't ask. He just assumes, and then makes it worse by persisting along this path. Then, quite naturally, you react by pointing out the inappropriateness of his remarks (behaviour?).
If the persons involved in a social exchange (eg. date) discover that they are sufficiently interested enough in each other to want to have a few more "get togethers", then that opens the door to further exploration "by mutual consent". This is when they should try different things, different environments (eg. restaurants, dances, movie theatres, picnics, group dates and social gatherings, meeting family members, going to church together, and such). This affords the couple many and diverse opportunities to see the many sides of the other person, from which they have sufficient information to be able to evaluate and decide if they are still interested. It the answer is still "Yes!" then the relationship, which now becomes courtship, can be pursued further. If the answer is "No!", then perhaps they should both agree to remain friends or acquaintances, and then move on.
If a woman has no interest in a long-term relationship in the first place, then she should be very cautious about approaching a guy in the first place, such as "I just need a partner to go with me to this wedding." The mere act of approaching and asking him out on this occasion is, in fact, sending him a signal that is probably implying to him a certain level of interest in him as a person, and even as a possible relationship.
There are certain types of guys who are dating with "no strings attached" who do it all the time, and think nothing of it. On the other hand, I would say this is not true for the majority of guys, especially the shy ones or the less popular ones with the ladies. These ones take things much more seriously, and so tend to read into things more than is really there. That is why it should be made crystal clear to him at the outset, when you first propose he accompany you, that this is merely a case of accompanying you as a "convenience partner" thing, and nothing should be read into this beyond that. "We are just good old friends, and that is all!! Understand?" And get him to acknowledge that up front. There must be NO ambiguity right from the get-go. If he acknowledges this up front, then you have a basis to remind him of that later if he gets out of line with his remarks or behaviour later, such as at the wedding.
Anyway, it really ticks me off the way so many of the male specimens of the human population don't know how to act with a woman. It's like they have all been programmed with this fast-food, instant news, and right-now self-gratification, that they think they can just fast-track the "male-female interaction" thing the same way. They need a good lesson in dating and etiquette, and should do their homework on how to properly treat a lady. If they did, they would discover they would be a lot happier, and would go a lot farther in their relationships and friendships with the opposite sex. IMHO.