As I went from thin and fit to fat, I grew a double chin. It was a weird feeling like all of the sudden I had a cushion around my neck. Sometimes I'd feel it jiggle a little or move while chewing. Soft and fun really.
Second how it gets in the way when looking down. It also makes getting dress shirt collar sizing right difficult, because just like a belly it can really thicken your neck when compressed.
Sometimes if I'm brushing my teeth energetically I'll feel it jiggle some.