It may seem like the standard operating procedure for many reading this article, but unfortunately, we often find ourselves in the minority towards such an issue.
Your personal image is not something that should take a break on an airplane. Yes, flights are long, seats can be uncomfortable, but just because you desire to be comfy doesn't mean you have to be sloppy.
I'm not advocating for three-piece suits, more simply, you should always aim for a sharp, smart casual dress code, and here's why.
Free up space in your suitcase
The nicest clothes quite often take up the most space. That swanky pair of freshly polished RM's, your blazer you don't wish to fold into a suitcase or carry in a separate suit pack - they have other uses. Nail the light packing game by wearing this gear instead. Couple those RM's with some chinos, a button up and top it off with the blazer to sport the perfect outfit for your flight. When you get on board, simply ask the flight attendant if they could hang your jacket up for you, to which they will almost always oblige (unless you're on Ryanair).
In the case of long-haul flights, there are definitely no excuses, just change your outfit when you're on the plane. If "Nah I can't be f*cked" comes into your mind, pull your head in, it seriously takes all of 2 minutes to duck into the bathroom after takeoff and get into something more comfortable. On the flip side, you'll have a fresh set of threads to change into before you touch down.
You may get an upgrade
Such a phenomenon is much less likely these days. It's becoming more and more of a challenge to turn on the charm and convert your sweet talking into a spot up the front. This is thanks to the abundance of frequent flyer programs and common overbooking practices from numerous airlines that are generally restricting your luck.
If you're dressed well upon check-in, however, your chances - despite slim - are significantly higher. If an airline is looking to upgrade the odd lucky person, an "SFO" may be typed into the system next to your name - 'suitable for upgrade.' You might get a nice surprise at the gate, you might not, but what we can confirm is that you'll never get anywhere near the single digit seats if you're in a Bintang singlet and thongs.
Look good, feel good
Fewer words of wisdom have ever been truer. Flying is still a classy affair, so you should dress for the occasion. If you dress like a slob you'll feel like one when you step off that plane.
You never know who may sit next to; first impressions when flying are more important than usual. What are the odds you're seated next to a high profile executive or maybe the love of your life? You're not going to get a job offer, pitch to a potential investor, or lock down a first date looking like Shrek.