Public restrooms can be uncomfortable places and this is a prime example why there's the unwritten man law of staying at least one stall away if at all possible. Of course it isn't always possible to maintain the one stall rule and sometimes you're forced to take a piss well within arms reach of another person. Some people are just curious, they don't mean any harm and perhaps merely forget proper bathroom etiquette in a moment of excitement. My only advice is don't panic or jump to conclusions. I'm sure there's a reasonable explanation. Just remember; absolutely no one wants to have sex with you.