Thanks for you replies, it lifted at least a tip of the veil of some motives for me.

When my eyebrows began to lose their natural darkbrown colouring due to greying I didn't recognise my facial default expression anymore, so I got them tattooed. I like it.

Another form of self expression. I don't mind it.

For me, I like them and don't like being the same as everyone else. you just answered your own question. people all decorate themselves and always have with clothes, makeup, tattoos etc. some do it to blend in and others do it to not blend in. I do the things I like whether I blend in or don't. everyone isn't doing it to please you or not.

Why are people different?

Once you have worked that one out, you will be on your way to an answer.

I don't like tattoos or overly-eccentric piercing. I also don't care for strange hair dyes. I find it unattractive/unappealing. I don't get it. But if that's someone's thing I guess that's fine, I realize that others disagree and do not want to police them.

I got my ears pierced in elementary school. When I was 28 I got my first tattoo and it’s for my kids. Couple years later got another one that is both for my dad and my kids. Several years later got my kids initials tattooed. Then I got the cartilage on my ear pierced twice. About a year ago I got a stud in my nose and a few months ago got another tattoo for my love of reading.

My youngest has asked if I’d get a mother/daughter tattoo so I’ll most likely do that and a 1/4 sleeve is not out of the question.

I’m 44. I completely get how some people don’t find it attractive. I don’t judge them for not having tattoos and piercings and expect them to not judge me either.

I had a guiche (perineum) piercing done a few years ago. I was told it would feel nice when I walked, though the reality is that I rarely even notice it's there. One time, when I put bigger jewellery in, it created a pleasant sensation for about half an hour. Then I got used to it again.

I chose the guiche because it isn't obvious unless I'm naked (it's only obvious if I am naked, if I spread my legs or bend over.) And I just fancied ticking an intimate piercing off the bucket list as an experience (you only live once) while at the same time not being brave enough to have anyone shove a needle through the really sensitive bits.

Pain-wise, the actual moment of piercing hurt less than having a blood sample taken at the hospital. Though it was sore and had to be regularly bathed in saltwater for a few weeks afterwards.

I'm unlikely to bother with any more piercings, but I do keep this one in, even though it doesn't create much of a sensation. A jeans pocket tattoo (about 3/4 real size) on one of my buttocks is very much on the horizon (I plucked up the courage to do it in December, only to find my local reputable tattoo place has a 6 month waiting list.) Again, to have had the experience as much as anything.

I am heavily tattooed (arms, chest, torso, hands, legs) I have a pierced nose, 4 tunnels in my left ear, 1 in my right, a ring through the top of my left ear and what is commonly known as a 'Prince albert'. I no longer have a pierced eyebrow or nipple but did at one time.
In all cultures that I can think of people do and have always decorated themselves.
Why do I have them? Many reasons but mostly I like them. Simple as. Is it hugely different from any other kind of jewelry?
All the reasons you give in your opening post are about right. Decoration, sexual enhancement, group identity... yes people are beautiful as they are but that's not the sole reason people do it. People don't wear a wedding ring to make themselves more beautiful, for example, but to say something to themselves and others who understand the symbolism

I tell my students that I'm a trend setter. I have no tats, piercings, or wild hair.

I can't really say regarding piercings in interesting places, I only have three each in my earlobes. I prefer tattoos (I've got two and am planning more) because, frankly, I find tattoo aftercare easier than piecing aftercare.

In my opinion, the body can be a wonderful canvas. One just has to be very choosy about what is put on it permanently.

If I could figure out how to insert photos here (I'm using a tablet, not a computer) I'd paste a picture of Elaine Davidson who, according to Guinness, is the world's most pierced woman. She currently resides in Edinburgh, Scotland, and my daughter and I saw her there, on the Royal Mile, when we visited two years ago. She was truly something to behold. I cannot look at multiple piercings like that without a shiver going through my body. I cannot fathom how people endure what seems to me must be such an incredibly painful process.

You've just named all the reasons they just to different degrees

Nobody hid the National Geographics from me when I was growing up, so as a youth I saw people of all shapes, sizes, and colors wearing (or not) all manners of clothing and adornment. Stacked rings stretching out your neck. Sticks stuck in your face to resemble jaguar whiskers. Women walking around with no shirts. People walking around with no clothes at all, or only loincloths. Elaborate hairstyles. Huge, weird, complicated hats. Facial tattoos. Scarification.

I learned that just about anything can get to be "normal" for people. And from that I surmised that if just about anything can be normal for someone somewhere, it can't be "wrong" to do pretty much whatever you want in terms of dressing and decorating yourself.

At various points (not all at the same time) I had 3 piercings in each ear and pierced eyebrow, bellybutton, tongue, and labret. I wear no jewelry now. I don't spend time thinking about what's behind others' adornment choices. I notice, appreciate--or not--and move on. It's as big of a deal to me as whether someone is wearing stripes or solid.

To stand out , I believe.

No clue-my 22 yr old and 35 yr old daughters are into tatoos but not piercings thank goodness. I have a personal problem with tatoos, don't even have pierced ears anymore.

for me it is a way of making myself look on the outside, how i feel on the inside. it has nothing so much 2 do with being beautiful 2 others, but being beautiful 2 yourself. also, in my case, my tattoos and piercings each represent an event in my life, or something i overcame, or they are 2 represent someone important that i lost. they are a badge of honor i wear.

It just makes them happy
very person is happy in what ever they like doing
piercing is one of them