A person should always be able to see you before they smell you.

The first, most obvious offenders are smokers.  That is a smell that invades your car, your clothes and everything around you.  It can be a difficult smell to get rid of.  It is also one of the most offensive smells to non-smokers.

The second is the person who seems to have showered in their perfume/cologne.  Even the best of smells can be nauseating when they are too strong.  If you don't know how much to put on, don't put any on at all.

The third is an often overlooked mistake - smelly lotions.  It is nice that you can smell like any fruit, season or emotion by simply moisturizing your skin, but that aroma can be just as strong as the perfume/cologne shower you just avoided. 

I've never heard anyone complain that someone didnt' smell like anything, but I've heard many complaints of headaches, migraines and more just from someone's smell.  To make your life simple, I suggest avoiding all smells.  If you feel the need to spray something - try Febreeze! :)