Hmm. . .,
That argument cuts both ways. I've spent many hours of personal time on work related activities. I can't count how many Saturdays, late nights, and homework I've done for the companies I've worked for. Never complained about it either. But I had a boss who got on my ass for taking a shit one day. I told him that I was going to break his teeth out of his skull if he ever got in my face on that shit again. He never brought it up again.
I let all my bosses know that I will do them severe bodily harm if they f*** with me on the job. I can get away with this for two reasons. The first is that I am a great worker. The second is that I don't care if I get fired.
The bottom line is that a boss will f*** you if you let him. People abuse their power, so you have to remind them just how powerless they really are. I can be a great guy or I can be a real mean son of a bitch. It's all up to them.
Most of my bosses end up liking me. It works. Trust me on this.
Out.