My 2 Siamese algae eaters are a little bit territorial with each other. Generally the slightly larger one will chase the smaller one to the far end of the tank, and then leave him alone. This usually happens around feeding time. It doesn't seem to bother the smaller one much, as sometimes he'll stop to grab a piece of fish food even as he's being chased.
15 minutes later they might be grazing on algae side by side.
I haven't seen them chase my Otocinclus, or my glowlight tetras. My bristlenose doesn't ever get chased, not that he'd give a damn if someone tried.