That's essentially what Worf was to do. He hands Kurn the weapon. Kurn stabs himself, hands it back, then Worf wipes the blood on his sleeve. Klingon howls follow.There's assisted suicide in some states now. The state I'm aware of, it involves a terminal illness, at least two doctors' signatures, and the ill person must be able to do the key action themselves - an assistant can prepare the liquid and put it in the patient's hand, but the patient has to put it to their lips and drink it themselves.
As for terminal illness, the practice of disgraced officers falling on their sword(or pistol) has been practiced throughout human history, particularly among western nations, and into the 20th century.