It's not too often that Ianto and Jack have a serious argument. I can see Jack feeling a bit jealous, but it is kind of odd that Jack was taking a step back and watching everyone else have fun. I'm glad that they patched things up and had a good time for the rest of the evening.
Author's Response: Perhaps Jack was in a bit of a contrary mood. he's usually the popular one, but everyone was wanting to dance with Ianto and Tosh, when they weren't dancing with each other. When Jack gets jealous, he goes the whole hog! Thank you.