The first scenario, I wouldn't worry about it at all, frankly - didn't really impact anything, not a huge deal.
Now if it was something like a passenger smoking in the lav or something serious regarding flight safety, I'd notify the crew or whatever else would be appropriate.
The second...I don't know, you could say something to the guy but I guess the damage was already done depending on what he touched exactly. Probably just avoid whatever he touched and...try not to think about how many people do this who you don't even know about!
