Yes, Rush Limbaugh should apologize for calling the young lady who defended Obama's cotraceptive policy a "slut". It was rude, crude, and ungentlemanly.
However, he should wait until Bill Maher publicly apologizes for the various things he called Sarah Palin--although Palin is probably tougher, more thick-skinned, and more mature about being in the public eye than the tender young liberal Georgetown law student.
What gives the political Left the idea that it's verbal mud-slinging, ad hominem attacks, vicious rumor-mongering, borderline slanders, shouting down of opponents, and similar routine disregard for the free speech of opponents is acceptable and normal? Well, maybe such "normalcy" is one reason why the Left needs to be kicked off the public stage and why its media needs to go into bankruptcy as soon as possible.