How to deal with other unruly kids and parents who do nothing?

How do you handle toddlers who won't let your child play and parents who do nothing?

I was at this park/cafe play area with my 17-month-old. At one point, she and one older toddler were the only kids there. There were loads of toys available, including about five of those little ride-on cars.

Every time my daughter went to climb into one, the other boy would sprint over and and try to aggressively get in it first. We'd move to another car, and he'd do exactly the same thing. It wasn't just the cars either—he'd do it with pretty much every toy she showed interest in.

His, I assume dad, was standing nearby watching the whole thing and never said anything. It wasn't even like he wasn't paying attention he saw this.

If my daughter behaved like that, I'd step in and try to explain that the toys are for everyone and that other children can play with them too.

I was getting an overwhelming urge of giving this kid a telling off and picking up one of these little cars and chucking it at the other dads head. I didn't, I just took my girl and left.

How do you stay calm in situations like this? Do you say something to the other child? To the parent? I feel as my baby is getting older I'm going to be put into these situations more and more often.