I used to say the 340i I had was bipolar. It could sit in eco-pro at 70mph on the motorway, be as comfortable as anything(did once drive about 8 hours through France in it and had no comfortability issues) and it would just sip away at 43mpg. Then you could drop it even just to Sport(not even Sport+) and it was an animal. Of course, that isn't down to the individual one I had; they'd all be like that.
Miss that thing. Would love a 140i, but... I do like 5000 miles in my Fiesta so I just can't justify the price.
My parents do it on occasion, generally based on the model or numberplate. Ie the Corsa Comfort was 'CoCo', the Volvo's numberplate ends in YKC, So it's called Kasey(Casey?) I tried it with my current car, numberplate ending RTZ. A doctor in German is an 'Artz', so I tried to call it the Doctor, but it just doesn't work for me.