What does it mean when you put your thumb round your chin and your finger up your face? (it's a pose)?

my dad was looking at my pictures on facebook and asked me what the pose we did meant, and I said we made that pose because it's the pose that all the 10 year olds do and they think they look cool and he said that it means something else. It's basically when you make an 'L' with your thumb and finger then put your thumb on your chin and your finger goes up your cheek. What is it's rude meaning:L?