1 Picking your teeth in public
Actually, this is extremely useful for your dental health. Helps to remove the food that may cause tooth decay if it stayed in or between your teeth.
2 Nose picking
Doesn't have particular health benefits, besides probably removing some snot containing bacteria, but is very pleasant and relaxing.
3 Mouth washing during meal
Washing your mouth with your drink is one of the healthiest bad habits as it helps to wash out the food remains. It may be especially beneficial if you do it with green tea. Green tea kills the bacteria that cause dental plaques and bad breath and increases the acid resistance of tooth enamel.
4 Head scratching
For many people this is a "thought promotion process" habit. Also, as a possible alternative to scalp massage, it stimulates the scalp blood circulation, which is beneficial for hair follicles. Recent research in the Journal of Investigative Dermatology found that, although scratching an itch feels like a pretty primal activity, there's some fairly complex communication going on between the skin and the brain - even when what we're scratching isn't actually itchy
5 Finger sucking or nail biting
This may have immunity boosting effect. There are lots of bacteria on our hands. Getting the portion of these bacteria regularly makes you more resistant to microbes. And if you combine this with the nose picking, the effect becomes even stronger.
6 Bum scratching
Although not aesthetically pleasing, it helps to get rid of nasty itching.