I worked at a firm where an after work session of Half Life was standard after a long day. Blasting your boss in the head with a weapon of your choice was very therapeutic. No problems with this after work but when it came to a lunchtime session it was a different story. Initially no problem but then there was a senior manager showing someone round and they wanted to walk through the department and out the fire exit at the back. He sent an email explaining that it was the lunch hour and we were free to do what we wanted. The company computers and network were not to be used between 9 & 5 for playing shoot em ups. He didn't have any problems after work but it looked bad if clients saw it.