For those who just don't get how to manage those socially awkward situations, here are some instructions to make your life easier.
Situation: Your friend's got something in their teeth.
Resolution #1: Just pull out a toothpick or a flosser from your pocket/bag/purse and nonchalantly hand it to them. Keep talking seamlessly so as not to draw attention to the unruly stuck spinach.
Resolution #2: As quickly and flamboyantly as you can, pull out your compact mirror, open it and shove it into their face, laughing hysterically. Sometimes you don't need words, just laughter.
Situation: Buddy's got a booger hanging on.
Resolution #1: Just hand them a kleenex, 'nuf said.
Resolution #2: Try this sentence on for size, "Dude. You've got a hanger" while motioning your own nose.
Resolution #3: Just start incessantly playing with your own nostrils until it catches on... some times things can be mimicked subconsciously and with any luck, it will knock the booger loose... problem solved.
Situation: Your friend's showing their crack as they sit down in jeans which are too low/small.
Resolution #1: Say nothing. This isn't really your problem, unless you find it embarrassing to sit next to, in which case, try resolution #2.
Resolution #2: Jump up and shield your friend's behind with your coat yelling "There's nothing to see here folks, move on, MOVE ON!!" Next time, your friend will likely think twice about wearing better fitting pants.
Situation: Your lover's face has suddenly developed a giant whitehead and you can't take him/her romantically anymore because it's too distracting.
Resolution: Literally the only thing to do here is to gently just start touching their face, and offer to pop it for them. If you can't pop your lover's pimple, you aren't meant to be together. Chances are, they'll go off into the bathroom and do it themselves. But definitely point it out to them, they don't want to be a turn off.
Well, hopefully that will help you out in some potentially awkward moments. Best of luck!