Or something

Why, when people feel threatened by you taking photos, do they say, ‘Can I help you?’
 
‘No, you can’t,’ I want to say, ‘I was managing much better before you turned up.’
 
Instead I sigh and say, ‘Here, do you want to look? I’m not a threat to you or anyone else.’
 
‘Oh, no, I never said you were a threat.’
 
‘I’m just looking at the shadows of the bikes on the railings.’
 
‘Are you a photographer, or something?’

What is their problem?