Aaron Hernandez -- 'How Much Is a Hit On You Worth?'

When TMZ asked Aaron Hernandez about a hypothetical bounty on his head ... all he could do was smile and laugh -- then again, the footage was shot nearly 4 months before he allegedly killed someone.

We found this clip showing the former New England Patriots star leaving Saddle Ranch on March 5 ... sporting a big ol' smile as we asked him about the NFL bounty scandal.

Now, of course, the term "hit" has taken on a totally different meaning ... as the 23-year-old faces murder charges in the slaying of 27-year-old Odin Lloyd.