@aidan,
Laughing at people is rude. If he/she wants to walk around with kleenex stuck up their noses, then they're allowed to. Snickering about it is allowed, too... just not in front of them.
They obviously have some sort of medical problem and this is the way they're dealing with it. If it were me, I'd use smaller bits of kleenex so it wasn't so obvious, but maybe they've been doing this for so long that it's their 'normal'. Either way, they don't deserve to be laughed at. Most people are sensitive that way. In my case, the woman was a stranger to me and there's no way I would have spoken to her about it.
I worked with another woman who would colour coordinate everything, from her eyeshadow down to her shoes and stockings. So, if she wore a blue skirt and yellow blouse, her eyeshadow was blue and yellow, her shoes were blue and stockings were yellow. She'd have a yellow sweater and yellow and blue jewellery. She nearly always looked ridiculous in her strange colour choices... but I don't think anyone ever commented on her outfits... she was happy with it and how did it affect us? Not at all.