It depends on the situation.
Moderate to severe line jumping: People in my group have guts and will say anything to anyone.
Impatient line jumpers: Use a physical approach. While waiting for FoF, we stopped the line from entering the already packed station. A group of teens cut some people and slid past us to the back of the train. We noticed they were now heading for the front (our intent) so I turned sideways and put my hands on my hips making a physical barrier. The determined leader did not get the point, so she tried plowing through me like we were at a concert. At that point, I just walked to the front (ahead of them though) and my sister couldn't resist calling her out.
Light line jumping from young kids: Usually ignore; don't want crazy mothers screaming in my face. Example: Yesterday at Soak City a young girl cut two people (my sister and I) for a slide. Because she was so young and didn't know better we let it go. A few weeks before while waiting for Calypso at CP two young girls behind us walked in front of us when the ride op opened the gate. Again, they were young, and we got on the same ride anyway.