Help Me Be a Nicer Person

So help me out here, you guys.  I have a close friend at work who is driving me a little nuts.  She's a really sweet girl and I do like her a lot, but she has some annoying habits.

Is there a polite way to say:

"If you can't stop yawning every two seconds, can you at least cover your mouth?"
"This music blows goats.  If you don't turn it off, I may go postal."

Also, what is the proper response to "I just can't seem to keep any weight on!" (She's a skinny blonde, of course)?  Because here is how that conversation goes in my head:

Barbie: I'm letting myself eat anything I want, because I just can't seem to keep any weight on!
Me: *eyes narrow* *growls low in throat* *pounces on Barbie, ripping her limb from limb*

Since that's prohibited by law, and I do genuinely like the girl and would miss her if I ripped her limb from limb, I usually just stare at her and blink a few times.  Then I try to remind myself that we all have body issues, whether we're dealing with too much weight, too little weight, or weight not in the right places and her body issues are just as legitimate as mine, as annoying as they may sound to me.

Help me stay out of jail here, people.