It's not lame if both players agree to it, how do you even know if either of them have played on any those maps before? Even if they have used the same map 100 times both players stand an equal chance because there will always be different gameplay.
So no, I don't think it's lame, of course YOU have the choice to say no to it if he picks it against you.
If it makes them happy, why critisize them?
Anyway, off-topic, get searching for those shots !