My sister had never cut a grapefruit before. She'd never even seen one get cut. So, when my mother tasked her with preparing the fruit, she was able to invent a cunning new technique that takes absolutely no time, but allows you to eat all of the flesh but none of the pith, without accidentally getting a sticky seed in your mouth! Here it is.
Step 1: Cut in Half Along the Prime Meridian
Divide and conquer! Unseam it from nave to chaps. I mean, cut the grapefruit from top to bottom. Um, just look at the picture.
Step 2: Cut Into Slices Latitudinally
Now, simply slice the grapefruit into wedges. The benefit of this method is: After you eat one triangle of the pulpy fruit, you can very easily peel back the section of pith guarding the next. Also, the seeds are easily flicked away.