Short answer: Nobody.
With Bragg, it was a warning not to cross him. Had Bragg thought Forrest was going to kill him, the matter might well have been settled in Bragg's tent then and there. Bragg was not a coward and feared no man.
Hood - Legend has it Forrest told him if he was a whole man he would whip him within an inch of his life. Maybe he said that, maybe not but it was not a threat but an angry response to Hood's plans for the battle at Franklin.
Forrest didn't threaten to kill people. If anybody got killed by him, it was because they gave him no other choice. Even Gould, who shot him and was then stabbed by him and died, was not an intended casualty. He seldom started a fight but sure had no difficulty ending one.