It was a pretty rare thing for Tony to not have any words in response to -- well. Literally anything. He was quick witted and was always willing to put his foot in his own mouth or dig his grave a little deeper in order to say something. But in this instance, he was just offering Steve a wide eyed, surprised little expression -- like it was taking him just a little bit longer to digest what he was saying.
Probably he would have thought of something eventually. It also probably would have been incriminating. Just about as incriminating as getting his hands twisted up in Steve's shirt and raising his head to meet that kiss.
So it was just as well he didn't say anything, anyway. His mouth was busy.