I've seen my yellow will nibble at the cleaner shrimp, I've also seen him nibble at the base of a feather duster who was "in the wrong place, at the wrong time."
Tangs graze all day, and just seem to nibble on what ever they can. I moved the feather duster out of the area that he patrols, and he's completely ignored it. If I see him picking at something he shouldn't, I just put some nori, or a pruning of caulerpa from refugium into a clip and toss near one of his areas.
Then he'll nibble that every time he swims by it. Keeps him busy when he's bored. I usually do it 2-3 times a week. | 
