Yeah, the bulk bins (and to some extent produce) bug me quite a bit, since there's no way to pay for it -- do you tell the cashier "by the way, I had two or three gummi worms before I filled the bag, so add their rough weight in?" With produce, I think it depends; if you actually buy the grapes, no harm no foul, but if you don't, you've probably made that bunch of grapes as unpurchasable as an opened, half-consumed box of Triscuits sitting at the back of a shelf where the semi-consumer prays it will not be noticed by the Supermarket Police.
Also, I think there is just something hell of sad about an obviously middle-aged or elderly gentleman doing samples at the grocery store -- like the happiest thing that has happened to him all day is a stranger pouring half a beer into his mouth. The apparent enthusiasm is very sad indeed.
(I don't know why there is not the same sense of sadness around middle-aged or elderly women doing such a thing; is it because we assume that women of such an age are "part-timing" after having been full-times wives or mothers, but that men must have spent their entire productive lives at the supermarket or have had no meaningful vocation at all? Man, now this is going to bug me.)