My six line is friendly to all in my tank, even have a corisse wrasse and they don't fight. I bought a fairly wrasse and it attacked it and killed it, bought another but quarantined it, and the sixline kept trying to get at it, so I returned the fairly.
Wierd how it is fine with all others, the sixline was the first fish, never bothered anyone until the fairly.
So answer to your question, yes they can be aggressive.