I can never be a personal shopper. I don't know what to buy for adult boys. The best gift that I can think of - ties. If they don't like the color or design, that's their problem and not mine anymore.
Gifts for girls are easier. Just look for the latest trends and it will be the best-gift-ever especially for teen girls. Teenagers are still confident in wearing and using anything, even if they look weird, compared with older girls. As long as its the latest "in thing", they won't hesitate to use it.
Every gift-giving season, boys are my problem! What about you?