I guess Kisha and Jen were just really angry Luke pushed them, and when they reached the next clue box, Luke went head on even though Jen was still the first at the cluebox. I could understand Margie's protect for her son.. but this doesn't mean Kisha/Jen are totally wrong for laughing at Luke. I am sure when we're pissed off for certain times in our life, we do things that are not very nice as well.. this just happens to be one of those "bad" moments for Kisha/Jen.. but I still believe they are very nice people in real life in fact, same goes for Margie and Luke.
I kind of disagree with the observation that "Luke pushed them" at the first shown clue box (using this phrase since we don't know what is the actual first cluebox). Per a previous message, I stepped thru the promo on my HD DVR. Luke was at the first shown clue box trying to open it. Jen is approaching at a run several steps behind. What I saw was, Jen either pushing Luke or using Luke to stop her forward motion or possibly trying to prevent Luke from backing into her since he had actually had gotten the box open as her hands touch his back. Remember Luke can't hear Jen approaching! Jen then goes around to Luke's left as his brings up his left elbow, shoulder and hand with the CLUE in his left hand. (You can actually see the clue envelope.) Luke probably did hit Jen, not sure whether it was intentional or not. After all either 1) he didn't hear her running up behind him or 2) he may have known she was behind him since she did touch him and was "defending" his space. After all he can't yell "stop it". If Luke intended to hit Jen, I think Luke's feeling was that he arrived first and should be able to get out of the way by himself not be PUSHED out of the way. You can then see Jen fuming in the taxi and saying "game on". Obviously, in Jen's mind, she had no fault in the cluebox scuffle, when clearly she started it.
At the second shown clue box, both Jen and Luke are clearly over the top, body blocking and scuffling all the way to the clue box. To me, it seems as if some other things to continue the escalation in "bad feelings" have occurred between the two boxes. Or may be they are just being extremely competive.
As I said before, I find K/J's snickering extremely disturbing.