Aren’t Sikhs normally peaceful, but they’re vicious fighters if provoked?
They are lovely people, except when occasionally bombing passenger planes.
Based on my personal experience, yes to the first part. Although I've worked with and for Sikhs, I've never provoked one, so I can't answer to the last part.
I suppose if I had provoked one, I might not be around to answer to it either...
See my #46. They are peaceful and not permitted to harm any living being (human or animal), but they are permitted, even required, to use force in defense of the innocent (for example if a criminal is beating up an old lady and no other way to save the lady, duty requires a Sikh man to come to her aid by using violence, if necessary, against her attacker) or for the common good (say, against tyrannical brutal ruler) if no peaceful means will suffice. I have heard they can be fierce fighters, but never witnessed it myself.