So, asking for alternatives to what you consider ethically questionable makes you a jerk then? And opression is not to be questioned if getting rid of it and its externalities would cost something?
The guy who went there for ice cream is more to blame than the clerk in this issue.
Second, how did you get the impression he was "taking it out on the clerk"? He simply was asking for an alternative method to access the WiFi and expressing his concerns about his privacy. Are you also to blame for taking it out on the clerk if you ask, for example, whether you might open some window because you think it's too hot or too cold or whatever?