Hmm, last time I checked being a teenager was hardly a criminal offense. Of course, from what I remember of my teenage years (aargh, I am getting way too old), embarrassment was far easier to achieve.
Anyways, my tips would go along the lines that others have suggested:
Choose a charcter concept (rather than a cool set of abilities)
Design a character to fit that concept, even though it may not be the optimised set of abilities.
As part of the character creation process write up a character history, use that to decide on is motivations, goals, family etc.
Try to keep away from the cliche - "I was orphaned when orcs killed my tribe and now I adventure to kill all orcs and avenge my family" The character history can be varied, and provide direction for your character.
If physical play acting/accents aren't your thing, don't do them! The game needs to be fun and not everyone is into acting style role playing. Rather let your characters actions show his personality and goals, let those in between combat scenes be something significant instead of just collect the gold from the king and find the next adventure (of course you need a DM who will support this style of play)
Just my 2c worth, hope something is of use to you.