Cigarette butts flicked from cars piss me off to no end. I suppose it's always been an issue, but when cars still had ash-trays at least some people were using them... if only to dump the contents in a parking lot somewhere.
I'll add dog shit to the list of piss-offs. Perhaps not litter, but definitely belongs in the trash. There are great dog owners who stoop and bag it, but many who do not, especially in winter (because, hey... it's going to be covered in snow and of course vanish into nothingness
). Walking along paths such as those on the mountain brow in Hamilton on a spring day, just after snow melt, is an adventure for the sense of smell and a test of foot reflexes should one veer toward the path edge.