Out of curiosity,why are hetero males so oblivious to flirts?

Ok,i work with these 2 older men,who seem to be good buddies or something.I see than one seems to act different toward the other.One is married and the other has a girlfriend(i think hes bi),Ive notices that the one with a Gf tends to flirt with the married guy,but the married guy is oblivious to it.I think he sees it as friendly gestures or something.The one with a Gf will also show symptoms of jealousy when the other talks to this female(older female with a gallon of make-up on),they tend to flirt and all.So is it just this guy or are most hetero males like this ive noticed when i accidentally(i flirt without wanting to with both genders) flirted with straight males in the past they had no idea,or at least showed that they didnt know i was.Im pretty observant person so i noticed quite a few things.