Originating Down south ,this term refers to someone being pissed off to the point of pulling out a gun.
(38 Referring to a popular hand gun easily obtained at the local pawn shops)
"Man! I was 38 hot about that bitch scratchin up my car!"
being pissed off, hot. i.e. Hot as a stolen 38
When Brad walked in on us, he was 38 hot.