You are certainly entitled to feel that perhaps this joke was ab it over the top, though I personally disagree; especially if it was said with a straight face, thus implying a certain degree of deadpan humor in my mind.
However, I believe the important bit here is that while you may think the joke went a bit too far, I also think that you must realize that she put him into a situation where a joke was the only real option. The only question was what sort of a joke would it be. And of course as with all jokes, there is the possibility of the either joke falling flat or the audience deciding that there must “secretly be some truth there.” So basically, no matter what he said there would have been some sort of reply that might make you or your girlfriend feel uncomfortable. However, in the interests of education I will provide other possible scenarios.
Also, I will provide options, their downsides, and possible “hidden subtexts” that your or your girlfriend may pick up on; thus revealing the friends true feelings.
Think about it, she jokingly “asks him if he would take her out and what would he do with her.”
Would you prefer he say, “Well first I’d take you out to dinner at such and such for a romantic meal, then we’d walk along the beach and watch the fireworks before we head to my place where I have prepared the room with candles, wine and roses.” or something along those lines? This could still be a good joke depending on the relationship between the two of them and on his delivery but is exceptionally vulnerable to backlash if taken wrong?
Hidden Subtext 1: I’m a hopeless romantic who has been pining for you for years and who secretly thirsts to provide you with overblown romantic cliches.
Hidden Subtext 2: I’m gay. I have no desire to see you naked and cannot comprehend of a romantic relationship with you and therefore am using material from a movie I saw once.
Or, he could have just taken the ‘safe’ route and reply to her “joking manner” with a serious “No I wouldn’t take you out. Your my friends girlfriend.” Which probably would have killed the mood and left her feeling rather awkward and embarrassed at having been taken seriously.
Hidden Subtext 1: I protest too much. Your comment, though in jest, flies to the heart of my secret desires. I know I have no chance so I deny it all but you have no idea how much it paints me to hear you joke about this.
Hidden Subtext 2: I have no desire to sleep with you. I do however want to nail your boyfriend. I’ve just been waiting to have a boy’s night out and get him drunk enough to bend over my couch. It’s paisley by the way. The couch I mean.
What else? There’s always the simple, “Dinner and a movie.” Which, could still be delivered in a facetious manner but has the same risk as the first example of being taken as an honest proposal. The difference is that the first example is farther “over the top” and thus has a little more protection, though in both cases the potential for backlash is high.
Hidden Subtext 1: I am irritated by your shameless desire for attention you prancing bitch and thus, I choose to put no effort into my reply. Frankly I wouldn’t dignify your hopeless fishing attempt with a remark at all by your boyfriend is my buddy so to keep the peace I have to say something.
Hidden Subtext 2: I want you. I want you bad. I know that if I could only get you to watch the Seventh Seal with me, later at dinner I could so dazzle with my knowledge of Bergmen to the point where you would ditch your boyfriend and immediately drop to your knees under the table.
The last two main options involve an “over the top” positive or negative reply. The reason for exaggeration is to put both options out of the range of realism and thus keep emotions from getting bruised.
Here they are. Number One, the negative, “You? Hell no, you’re nasty.” In this case of course, the joke is that your gf is actually hot and they both know it. The downside is that people can be very self-conscious and your girlfriend my be deeply offended. There is also a second variant to this which goes a little more like, “You? Hell no, you’re nasty. How could I ever get it up for those perky breasts and firm hiney. I prefer my women with a little more sag. You know, something I can really swing from to remind me of my days at the playground.” This alternate also has a downside in that you or your girlfriend may be deeply offended by the fact that he noticed her perky breasts and firm hiney. Naturally, there are further pitfalls to be found in the subtext.
Subtext 1: Yeah, yeah. You have a nice body and when I first met you I thought you were good looking. That was of course before I realized what an evil skank you are… You’re a bitch and I’ve been wanting to say that for months. Frankly, you’re so much of a bitch that just the sight of you causes me great pain and I cannot conceive of how I ever found you attractive. I am just grateful for this chance to insult you to your face while camouflaging it as a joke.
Subtext 2: Yeah, Yeah, you’re nasty baby. Oooh, yeah I bet you are. You wanna get nasty with me? Yeah, yeah I bet you do. Oh yeah baby I love when you do that. You nasty, nasty girl.
Finally, we have option your friend took. Dinner at McDonald’s followed by wild monkey sex. This has the advantage in that it has elements of both “positive” and “negative” exaggeration. For the negative, we have dinner at McDonald’s. This is pretty much universally known as, “Not the way to get a women” in that it simultaneously involves being a] cheap b] classless c] giving no thought at all to what the women might want. This is followed immediately by the suggestion of wild monkey sex. The humor here is that this sort of attempt would generally be considered laughably inept and thus, funny if proposed in a properly deadpan or earnest fashion.
As with all of the options though, there are many subtexts of which I will give you only two.
Subtext 1 [which you discovered]: I secretly lust after you and am attempting to use humor to convey my real desires and one day nail you over my paisley couch.
Subtext 2: I dig clowns. I really dig clowns. Clowns are hot. I want you to put on a red nose, an orange wig and walk all over me with big floppy shoes while you smear me with dipping sauces.
All in all, SHAKES said it best. It was a joke. Sometimes jokes go a bit too far. Sometimes people misjudge their audiences. Your best option is to be briefly annoyed and let it pass. If it seriously bothers you or your girlfriend, the next best option is to use the approach SHAKES suggested. Don’t put him on the defensive.
Anyway Pedro, I just previewed and saw that you already noted SHAKES method for dealing with the situation [which, once again I believe is the way to go] so most of this post is totally unnecessary. In any case, I enjoyed writing it so I’m going to go ahead and post it.