This is kind of light-hearted but I suspect there's more than a grain of truth in it.
First of all, ask yourself: are you a slow, medium or fast cyclist? Are you expecting to pull away from the lights quickly or slowly?
If you are in the medium or slow category, and there's a fellow cyclist ahead of you waiting at a light - and he or she looks like they might be quick - don't edge in front of them. They were there first and will be annoyed at having to get around you.
Now of course it's not a hard and fast rule, and you can't judge a book by its cover. Someone wearing lycra head to toe might still be slow. And what if you're medium and the other person looks medium too? Or both slow?
But anyway, it is worth thinking about. And there's a serious point too - if someone is having to pull around you, they may be in the path of a car coming from behind.
I would also add:
- don't try to sneak down beside a bus or lorry, especially if you don't know how soon the lights will change
- it's generally polite not to hover right in front of a motorbike, especially if there's room elsewhere for you