Since we have the thread about things moving from “high-class” to “tacky,” I thought it would be nice to have a companion thread about the other direction. There are quite a few things that used to considered tacky or fashion crimes that are now not necessarily high-class, but certainly normal, at least by most people.
I can think of three off-hand:
Wearing hats indoors.
Wearing white after Labor Day.
Visible bra straps.
Oh, a twist! While unloading the dishwasher last night, I had a good time making a list of “high class” and “no class” items and behaviors.
We can start with visible tattoos…like on the neck. Most of them are tacky, but they are normal now.
Too much makeup. Seriously, when did we start putting on false eyelashes and heavy contouring to go to the gym or run errands?
Also, too-tight clothes. Buy the size that fits, not the size you think you are, ladies. Sizes have no basis in reality in stores.
Lack of foundation garments (for women and men). Ladies, that dress looks way better with Spanks underneath, unless you are 18 years old and have a perfect body. Gentlemen, you really, really need to wear a t-shirt under your work shirt. I do not want to see your nips, nor your moobs.
Why yes, I was in an all-employee meeting yesterday, why do you ask? 
wearing jeans. Till about 1970, it was a sign that you were a redneck.
Or , in general, wearing very casual clothing in public was once considered tacky. Now it’s normal to wear anything (including jeans) to , say, the symphony.
Yoga pants or other ass clinging tights worn as full on pants. I love some of the visuals, but it still strikes me as odd to display your exact ass shape while at Target.
Scruffy beard stubble. Sure, goes back to Miami Vice times, but in many professional settings you used to either have a beard or were clean shaven. The permanent two day stubble now seems more common, even for suit wearing job types.
Are pajamas in public now acceptable? I see them everywhere, not just in the 7-11 at 3AM on an exhausted father buying diapers.
For a non-clothing answer: TMI. Once upon a time, people kept personal stuff personal. These days it seems everyone wants to share their bowel movements, their sexual quirks, what they do in the shower, how much they puked when they got food poisoning… There really is a line between being honest and open vs. TMI, and fewer and fewer people seem to know where that line is.
Commercial air travel in a tank top, shorts, and sandals.
My personal favorite. If folks knew how clean their seat was they’d be wearing a space suit, not short-shorts & a sports bra.
Not that I have anything against short-shorts & a sports bra. On the right person. 
Throw sweat pants into the pile with yoga pants and pajamas.
Not “tacky” so much, but I remember being in junior high and fearing accusations that you dared to masturbate. It was something you’d vigorous deny and people would brand others with it as losers. Now every third comment on the internet is about “fapping”.
Granted, making jokes about “I fapped” is certainly healthier than using accusations of masturbation as a weapon of shame. But it’s still a pretty major shift in perspective.
As noted upthread, wearing casual clothing everywhere is a big change. I’m not that old (42), but I can remember getting at least a little dressed up to go out to a restaurant or – especially – church. If I had wanted to wear jeans to church as a kid, my parents would have had none of it. I don’t go to church very often anymore, but when I do, I notice that people are much more casual than I remember being. And, when I started my career in the 90s, wearing a shirt and tie to work hadn’t completely gone out of style. But almost no one does that anymore. I kind of miss ties, and just a generally more formal workplace.
The other big example I can think of is porn. It used to be something no one ever talked about, and you had to deal with some skeevy guy in a dirty shop to get your fix. Now, it’s just… everywhere.
Linoleum. Or has it changed again already?
I seem to remember masturbation becoming “normal” to talk about around the time Beavis & Butthead came out. Could be that it just became okay for my friends and me to talk about it humorously once we saw B&B talking about it humorously, but that’s when it lost its taboo in my experience-- early 90s.
I’ll be in my bunk.
Not that there is anything wrong with that.
Reminds me of a quote from a Life in Hell cartoon:
“Masturbation is nothing to be ashamed of, but it’s nothing to be particularly proud of either.”
Bringing children, especially toddler-isn aged, to social events or restaurants.
Cell phones in theaters. When I was growing up NO ONE brought cell phones to theaters. Not a single person, ever.
Yes, but that wasn’t because they thought it would be tacky, Grandpa.
Still tacky. Same for overcoats.
Reading at the dinner table was a big no-no when I was a kid, but luckily the rest of the world has discovered the merits of reading and eating at the same time.
Heck, it’s perfectly normal for me to see women & teenage girls wearing stretch pants to church on Sunday.
Being late. It used to be that people dreaded being late because of the social stigma associated with folks who were late for stuff. Now, 5 minutes late is the new “on time” and on time is for the chumps.
I never get on an aircraft without considering if I’m wearing the correct shoes to wade through twisted metal and burning jet fuel. No synthetic fabrics in my clothing, closed toe shoes only. I can’t believe people wear flip-flops on a plane. When after an event people tell me they had a premonition the plane would crash I always believe them, because I picture it on every flight. If I can’t get an exit row, I get as close as I can, I case the crowd to see who is going to hinder my escape, and God help you if it’s you, I’ll squash you like a bug on my way out. Air travel really doesn’t bring out the best in me. Would you believe I’m a million miler on two airlines?