Getting back to the OP, teenage boys are not known for their sensitivity towards others, especially when they are in a group and start behaving as a pack. They have absolutely no idea of the effect their behaviour is having on others, in fact it probably never enters their heads that shouting a comment at a complete stranger is intimidating, and five seconds later they'll have forgotten all about it and moved on to whatever other mindless entertainment is going to amuse them, as they drive around with no particular purpose.
It's all just funny to them, until someone challenges them on their behaviour, when they'l either laugh it off and move away, or become more aggressive towards the challenger, and if they've had a few beers it can escalate into violence, which they'll probably regret later, when they're sober. Incidentally, I have seen similar behaviour from groups of females out for the night in town, after a few drinks, when usually the majority of others around them are in a similar state, and I have felt intimidated if I've been on my own, just by their inebriated behaviour.
But whoever' doing it, it IS intimidating, whether it's a comment about a member of the opposite sex's appearance, accent, skin colour, or anything else. Advising someone to ignore it is understandable, but that doesn't tackle the underlying problem of a lack of respect for others.