I don't see what's charming about it at all and I hate the idea that people seem to think she owes him this date.
I also dislike the fact that she's interrupted multiple times, some where it's pretty clear she's about to say things like "if I'm not busy" etc. Also she seems not too keen when she's told she's going alone.
All in all this really grates on me, especially as people are now talking bad of her because she might not do it after all. She doesn't owe him anything, she was put on the spot (which in and of itself is rude, IMO) and now she's stuck either going on a date with a completely stranger, which she was pretty much forced into, or to look like the big bad person who doesn't wanna "honour a service man" and whatever else people are saying.
I hate this and I feel bad for her. 
I don't like this new trend of having to do everything someone in the military/veteran wants and give them your first born child in addition or "OH NOES you're a terrible person!" and get slaughtered in the media. If she wants to go on a date with a stranger, and he is a stranger, enlisted or not, that's up to her. She can't win- either someone else determines who she dates or she's vilified. Poor woman.
I agree. If this had been something private - the Marine had written to her, for example - she'd have had the opportunity to accept or decline without fuss. I imagine the usual response from celebrities is to decline politely and send an autographed photo. I certainly wouldn't want to spend an entire evening with a complete stranger - particularly not a complete stranger for whom I would be a *trophy*. For the man to make his invitation public was... well, not a polite move. (Although if he lost a bet, or was dared to do it, it's at least understandable. Thanks for making a lady you don't know the subject of your bet, guys.)
That Justin Timberlake intervened doesn't particularly surprise me. It can't have occurred to him that his co-star ought to be able to make her own decision, but he doesn't score very well on Feminism101.
I'm glad he's now received his own invitation-by-YouTube, but sadly, he won't be in the same position that Mila Kunis will be in, given the difference in the way men and women are generally treated. And he did, to a great extent, bring it on himself, whereas all she did was *exist*. Happily, I think the female Marine who invited JT is on the martial arts instruction team, so she should have no trouble keeping him in line!