I had a similar occurrence some years ago, at Rochester airport. Our S-76 (MAUM 11,700 lbs) was being refuelled on the helipad when a light fixed wing taxied up and parked very close by, on the grass. After the two occupants got out it became very obvious from their conversation that they were finishing for the day and one of them was an instructor. I was concerned their aircraft was too close to our helicopter but initially assumed and hoped they were going to tie it down, because I was going to have to lift off to the hover from where I was. However, they began to walk away. I stopped them and pointed out my concern. The answer I got was "frosty". But at least they did go back and tie it down. I could tell that the instructor was quite disgruntled but no harm was done.
At Royal Ascot (a major UK horse racing event for those that aren't familiar) I watched amazed and aghast as a single engined Squirrel hover taxied past me and others and then right over a line of parked helicopters. One of them, a Bell 222, despite having a blade tie down fitted, had its rearwards facing main rotor blade blown down hard onto its tail boom. I saw the tail rotor driveshaft cover dent right in then spring back out. I went over and saw the dent was now hardly visible but I was concerned what was underneath. I found the 222 pilot and told him to come and check his aircraft and showed him what looked to be little more than minor paint damage (I also gave him the registration of the errant Squirrel). I didn't meet up with him again until a few months after the event. He told me that the tailrotor drive shaft had also been badly dented and scored and the aircraft had to be grounded. Had the taken off, he would have been full of passengers. Had the TR drive shaft failed, especially at a congested helicopter parking area, one could only imagine what might have happened.
Another time I watched a pilot (coincidentally again a single Squirrel) hover taxy past me into dispersal, by actually taxying right over the right wing of a running Cessna 150 waiting to exit via the same holding point! The Cessna was blown all over the place and I could see the instructor hanging onto the yoke to prevent the control surfaces hitting their stops. Shortly afterwards I had a short discussion with the Squirrel pilot (who was wearing a nice dark blue jacket with four shiny gold bars bars on the sleeves and a set of wings on his chest) about the lack of wisdom of his actions; he came into our FBO to wait for his passengers. He said it was all ATC's fault because they told him to taxy via that route! Airmanship ZERO. All he had to do was hover taxy past the exit a few metres and allow the Cessna out first. I explained that if a solo student, rather than with an instructor, had been in command of the Cessna, he might not have been experienced enough to keep hold of the controls so well. Had the control surfaces hit their stops, a student might not have had the wisdom or experience to cancel his flight and get the aircraft checked. Again, this might have resulted in a pilot taking off with damaged flying controls. He shrugged his shoulders, didn't seem to get it.