I think it really depends on the type of jerk.
There are the jerks that are just immature and are even purposely being jerks because they think it makes them look cool. Obviously, these people know.
Then there are the jerks who don’t mean to be jerky and are generally just joking and messing around, but will acknowledge that they are being jerks when pointed out and then stop.
And then there are the jerks. My dad, for example, acts like a huge jerk in social situations in which he is bored or uncomfortable (particularly at doctors’ offices, for some reason). He comes off as the big, pissed-off, bad cop, “I really don’t want to be here at all,” impatient, asshole kind of jerk. It is completely obvious to everyone around him, and many people have pointed it out to him before. Yet, he vehemently denies it and can’t understand how he could possibly come off that way; he is totally oblivious to his jerkiness. Based on my experiences, the people who are jerkiest are generally the ones who are completely clueless about it.