I have 2 male opaline gouramis (fortunately not in the same tank), both are very aggressive. However, the gourami in the smaller tank is not as aggressive because there are a lot less fish per gallon in the smaller tank. Opalines are closely related to blue gouramis, so I'm not surprised that your specimen is also quite aggressive.
The male opaline in my larger tank has killed off at least 2 fish (both angelfish) and a flower shrimp. I have 3 dwarf gouramis in that tank and he loves to chase them around. The dwarfs are fairly peaceful, they really don't bother each other or any of the other fish. Over the past several days I've noticed some fin damage to all 3 dwarfs' rear fins (tail fins and back of dorsal fin), so I know he's nipping at them. If any more fish die as a result of the aggression, I'll have no option other than to return him to my local fish store (right down the road from where I live). Truthfully, the opaline should probably be in a much larger tank with the amount of fish that I have, but I'd rather keep what I have than buy a 70+ US gallon tank just to accomodate one fish's aggressive tendencies. I've added a few plants and have rearranged the tank a few times, and that seems to have helped matters. The male opaline is still aggressive, but only after a feeding. Most of the day he keeps to himself and stays in his own territory that the other fish have learned to avoid.
If your tank is large enough, and you can find them at your LFS, adding some female blue gouramis might help matters. Additionally, rearranging the tank or adding new plants might calm the blue gourami a bit. Try a few things first to see if it improves the situation, returning the fish should be a last resort -- it's certainly not fair to the fish to just flush it down the head or to kill it; fish are virtually brainless and don't know any better.