Should I be upset/concerned about this or am I overreacting?

It was birthday yesterday. I went out with a few friends, including a guy that I was interested in. Mind you, all of the friends knew this and the guy I was interested in probably knew this as well as we’ve been seeing each other for awhile. Anyway, towards the end of the night, one of my ‘friends’ (which we’ll call “Friend”) started making direct, obvious advances towards this guy (which we’ll call Guy). This irritated not only me, but most of the people I came with seemed to be irritated by this and wanted to leave almost immediately (which we did) and I haven’t heard of either of them since – which I think I’m pretty much done with both of them.

Although there were no established lines or statuses between me and Guy and I reserve anyone the right to hook up with virtually anyone they want, I just think that this was a very untimely, tasteless, inappropriate and low thing for not only Friend but Guy to execute on my birthday (and my other friends agreed). Am I being unreasonable? Should I just let “bygones be bygones” and pretend nothing ever happened or is this a lesson learned, that I should choose my friends a little more carefully?