I am not offended by any portion of your statement but I do believe it is patently false. I was recently told (to my face) at a bachelor party that "had I not met you I would've assumed your're a dumb jock" by a rather candid friend of a friend. Had I not already gotten to know him and witnessed how awesome he is, we would've definitely had words.
Stereotypes live and thrive through inherent bias, preconceived notions and a slew of other misguided assumptions.
Example: Fat people are lazy and self indulgent. A statement that is predicated on little more than a persons appearance.
Example: As mentioned above, we have all heard or witnessed the "dumb jock" stereotype. In many cases, bodybuilders aren't far removed from that false notion. The list goes on and on.
In regards to your "our lives revolve around bodybuilding and we think...." comment, I am not a bodybuilder but my musculature and size are mentioned often, very often. Do you believe that there is not even the smallest bit of conjecture our assumption behind the questions I receive? What other type of person our group are we permitted to query based on their appearance without social consequences? It is sometimes good, sometimes bad but it is alive and well.
The only part I agree with, in it's entirety, is the bold highlighted portion. This is what most subcultures in America can't get through their thick heads.