שמעו נא המורים, המן הסלע הזה נוציא לכם מים… (חקת כ:י)

We see that Moshe and Aaron were punished for calling the Jewish people “rebels”.  This is not an isolated case – other prophets through the ages also used harsh language to rebuke Yidden for straying off the Torah way.  The reason why they were punished is because it came at a time when the Jewish people were thirsty and were simply asking for water to quench their thirst – albeit in an obnoxious way.  Calling them rebels in this instance was perhaps insensitive.