Hope this isn’t old news – I came across this technique some some time back in a different context and adapted it to fit our purposes. Although illustrated it here with a bathrobe belt it works with just about anything of suitable length and flexibility, such as a necktie (not too wide or short), scarf, piece of rope, etc. I’ve used it mostly with neckties and so tend to think of it in those terms. Once it’s been prepared it’s quick to apply, comfortable (especially if something like silk is used), secure, and easy to remove afterward (usually).

Lay out the belt.
Fold down the bend.
Take one free end and pass it all the way through.
Take the other end and pass it through the opposite way.
Tighten the knot formed in the middle.
Insert hands (or feet) in the loops, pull the ends until snug and tie in a knot.