Airport Security? How to dress?

I have a flight soon and I want to get through airport security as quickly as possible because flying in-country (US) is already annoying enough for me, so I want to make this flight to Japan easy.

I'm arriving at Narita Airport. I'm going to wear a somewhat oversized shirt, something you would sleep in. And regular jeans, not tight not baggy and slip ons (slippers of some sort). Is that OK? Is it too casual? I'm flying Economy anyway.

I don't think you'll have a problem at the airport. But if you come to Japan in late fall/winter, T-shirt would be too light/cold. Don't forget to bring a jacket with you :)

OK! Thanks! So I wouldn't have to do so much taking of my shoes, stripping (joke), standing on one leg and hopping up and down while I recite my ABC's backwards stuff? It's just that's how I feel at the airport in the U.S., they make you feel like a criminal in your own country even if it's for the safety it seems a little unnecessary. Especially since I'll be traveling with my 3 year old son (first time traveling), I don't want it to be too hard for him.

Glico,

Security checks like that are for when you depart from an airport - not when you arrive.

Understand by end of October all foreign visitors to Japan will be photographed and finger-printed at the immigration check point like in the US. Surely, it makes things less pleasant while spending more time waiting in a long line.

The new fingerprint/photo requirement is supposed to go into effect 20 November, last I heard. I figure it can't help but slow things down.

Arriving from the U.S., if you're on a U.S. carrier you'll probably arrive in mid- to late- afternoon. Your arrival gate will be way out in the boonies; stand by for several rounds of moving sidewalks and escalators. People race like crazy here because they want to be first through immigration.
You'll pass the health checkpoint, which I've never seen manned and which seems to do nothing. There's a big poster up telling you that if you're coming from a selected list of countries, you are supposed to check in. I think I had a separate form I had to hand in, when I arrived from Thailand or Vietnam, I forget which. In any case, from the U.S., ignore this. Race through. Aroung the corner you will come to a counter with twenty-odd booths. Half of them are for Japanese passport-holders, half for U.S. The proportions may vary but the Japanese passport holders will be through and getting their luggage long before you will.
At immigration, somebody will check to see that you have filled in the arrival form, front and back. This has been important lately because sometime in the recent past they changed the form - it didn't use to have questions on the back. Now it does and many people miss them.
Step up to immigration where a very professional immigration guy or woman will flip through your passport, glance at you, and stamp your passport. Go down the escalator and voila, your baggage is probably already there because you were waiting at immigration.
You can dress any way you like.
Leaving Narita, your checked baggage will be x-rayed before you get in line to check in for your flight. At that point you are in a little 'check-in' area. Ticket & baggage claim, yadda yadda.
Go off to security, where I have never been asked to remove my shoes, but where you have to have your laptop out of its case and all that. Liquids in the bag. They have some kind of new scanner now that can analyze your bottle beverage (pet bottles & cans) to see if they are okay - who knows how that works? - They are very polite and will be very polite about if they need to open your carry-on.
Down the stairs to immigration once more, where you have no doubt already filled in the other half of your form - they stapled it into your passport when you got to Japan. A flip through the passport, a glance at the boarding pass, and you are through and can now browse the shops which are very nice these days.
Once again, you can dress any way you like.

Before moving to Japan, I had flown fairly frequently between San Francisco and Japan for the last 10 years and have found the security to be much more lax and expedient than the US (and much more polite and professional). As for the times I've flown into Osaka, I'm not sure there was even a line.

Overall, security definitely seems more relaxed in Japan.

Regarding the liquid identifier machine, I don't think they use it anymore. On my last two trips from Narita you weren't allowed to bring any liquids through security besides toiletries. And then you couldn't bring any bottles or cans on the airplane even though they would have been purchased within the secure zone.

It may be different when you travel, however, because security always seems to change every time I travel.

It is important to dress tidily when you come into Japan (or any country), as Customs officers do make judgments on you by how you dress. I came back from Laos wearing a tye die skirt, not really loud but an "ethnic" print, sandals and beads once and my backpack was given a fairly thorough going over. People I know with dreads/ visible tattoos say they pretty much always have their bag searched.

Having learnt my lesson I now wear jeans or black pants and a plain sweater or shirt to come in to Japan and I am not often searched- sometimes just a quick look into my bag if I am coming back from India etc.

The clothes you plan to wear sound okay- just make sure you look tidy.