That depends what it is. I would have to think a lot about it to figure out if I actually saw what I thought I saw or if I was jumping to conclusions. I usually think it is not by business and don’t jump to conclusions. My best suggestion is to stay out of it. Whether they are inappropriate or not, mixing in is also inappropriate. If you just can’t live with yourself speak to your Rav about it before you take it upon yourself to do anything.
The usual rule of thumb is if someone is doing something inappropriate in public they don’t care what other people think, so getting involved and mixing in will not help the situation. Giving tochecha to someone who doesn’t want to hear it and will not accept it is pointless and therefor only makes it worse so you are not allowed to do it. So maybe you jumped to conclusions and there is a viable explanation for what you saw or think you saw. So the best idea is to forget about it and don’t mix in. Let the people closest to that person and to the situation deal with it.