They've done this before
Spotted a couple of regular low-costers at the gate the other day.
They carried out a classic procedure to ensure getting on the plane early without having to pay extra for early boarding/ speedy boarding or borrowing a child to accompany them.
Here's how the move works. Firstly, get in the speedy boarding/ queue 1/ whatever the "first on board" queue is called by your airline, even though you are fully aware that you are holding Priority Z boarding passes.
Shuffle forward and when told told you can't board yet, look shocked, shuffle back a couple of feet , keep re-examing your boarding pass, nod sadly a few times and stand where you are, being careful to avoid eye contact with any of the 130 plus passengers who have spotted what is going on and are patiently waiting in the general leper queue.
When they begin their embarkation, shuffle across and board before all the saddos who waited patiently in line. Mostly Brits, as we seem to be the only nationality who view queueing as a courtesy, not a challenge.
Then, unleash part two of your "I'm going to have a stress-free flight" plan.
Occupy a window seat and an aisle seat, pretend you are strangers by keeping your noses buried in a book/magazine/newspaper and DARE anyone to sit between you.
If that works (and it usuually does), announce to the other passengers that you are, indeed, together, by removing your lunch, neatly wrapped in pristine aluminium foil, from your perfectly-sized cabin bag.
Who do I blame? Not these peeple, who are just cleverly playing the game, but the airlines for not allocating seats.