Check out our chat with him above ... where he stood by his fellow comedian, arguing people take jokes way too seriously these days. He told TMZ ... "Let comedians tell jokes!"

Despite overcoming addiction issues himself -- the "Jackass" star felt it was totally within JK's rights to call out RDJ on his troubled past.

Not only did the 49-year-old call hosting a "thankless job" ... he also reminded us that people who are sober regularly discuss their sobriety journeys, like at AA and NA meetings -- so why does it matter if Jimmy chimes in?

So ... it wasn't surprising when Steve-O declared Jimmy does not owe Robert an apology. Though, he made it clear he won't be following in Jimmy's footsteps, explaining he likes to make himself the butt of a joke.

Steve-O's stance comes a day after Jimmy sparked awkward laughter at the Academy Awards after calling "Oppenheimer" one of the highest points in Robert's career ... alluding to his previous court-ordered rehab stay in the early '00s.

Robert -- who has been sober since 2003 -- was a good sport about the dig ... making an "on the nose gesture" when the cameras panned to him. He also called out his struggles in his Oscars acceptance speech -- thanking his entertainment lawyer Tom Hansen for "trying to get [him] insured and bailing [him] out of the hoosegow" over the years.