Say someone you’re close to has some serious oral hygene issues… as in they seem to have forgotten how to use a toothbrush? How do you tell them they seriously need to find a toothbrush and use it not weekly but at least a couple times a day. I don’t want to be rude or hurt their feelings but… ewww! I have no idea how to bring this up.
Do they look like the yellow brick road?
I’d just say it straight forward. I had a friend that always “forgot” to brush his teeth in junior high. I gave him shit about it so he would brush his teeth.
“No girl is going to kiss you if they are caked with yellow” 
Is it relative close or friend close?
Friend- Introduce the subject by mentioning you’re wavering between a manual toothbrush or the new fangled ones with spinning brushes. Casually ask which they would prefer- buy it for them!
Relative- Ask them if they are ill. when they say no say its because their teeth (and probably their tongue) called long distance from the grime and they want to see sunlight again.
egads! how can someone not brush their teeth??!
Well usually the not brushing acomplishes that.
Hand them Altoids every time you see them.
Make a face every time they talk to you, when they ask why the face… tell them that their breath is not it’s best and a quick brush would help.
Just think of what you would like done if you were in the same situation.
Ask them how their last visit to the dentist went and how long ago it was.
Of course I’d just send them an Anonymous Email …
When he/she talks to you, turn your head the other away around. Then, he/she might get the idea that their breath stinks, or else that you have poor listening skills. Or look like you are gasping for air. I know these are rude, but it’s straightforward. Telling someone the truth, no matter how much it hurts, is the best policy. Lying is never good.