Bottom line is that every fish has a different personality. So even if the general guideline says that Picassos are not overly agressive, you can get stuck with one that is a complete lunatic. There is no 100% safe trigger. These are naturally agressive fish. But in my tank, 150 gal, the picasso was a lot less agressive than a niger and less agressive than a powder blue tang. On a trigger agression scale, I'd rate picassos somewhere in the middle.
You have blue throat, sargassum, crosshatch that are the least agressive. Then you have picasso and niger somwehere in the middle. Then there are the undulated and queen as most agressive. Clown triggers I would place between nigers and undualated.