Ever. Just don't do it.

I head to a client's site. In order to connect to their domain I have to let a sysAdmin f*ck with my machine.

Alarm bells go off, but I let the monkey have his banana.

To cut a long story short: it's the next day, many hours of work have been lost. Much frustration has been achieved. And I have a new rule:

It's the thin edge of the wedge. We let sysAdmin's screw with our machines today. What's next? Database administrators messing with our databases?