I agree with freetosee. As I was once a humble JW sister, wearing the 'modest' clothes befitting a woman on the ministry as was required by HQ, I felt mortified when I read this: i looked at her and w/o saying a word i started laughing so hard the guys in the truck started laughing as well... .
Without being there and seeing what happened, I don't know exactly what you were laughing at but I sincerely hope you did not humiliate her.
If it had been a couple of guys you were laughing at, especially elders who often think they are above everyone else anyway, I might have joined in the mirth thinking they could take it on the chin, but please remember that many JW women lack self esteem and already feel like second class citizens due to the way the Society treats them, and for a bunch of men to openly laugh at her in public might have been enough to push her over the edge.
I can understand why you did it, but at the risk of being a kill joy please think carefully before doing this again. Thank you