Actually you can always say that and it is always a compliment. It isn't always appropriate but always a compliment.
The Russian Shuffle is where you place a bar like you would in a squat over your shoulders (behind head) and then you get down into a squat position (ass to grass sort of thing) and then you pop up just until the legs are not quite parallel to the ground take a step forward (always remaining in your heels) and repeat.
Our gym is rather smallish so he took me out to this very long hallway in the building and stood in front of me and had me walk towards him. The hallway was so long... This exercise really hurts and there was more than one occasion that I paused and tried to quit. He yelled at me... I think he said something like "Don't you dare..." I was in so much pain. The good news is it took me back to the Marine Corp and I just went into warrior mode. I sucked up the pain and focused right on his crotch (that is where my line of vision was) and took one step at a time all the while imagining that I would physically crush him if I could catch. I was imagining how good it would feel to rip his head off or possibly crush him in the crotch and that is what made me go forward. So there we were in the hallway outside the gym, me in super pissed-off focus mode waddling down the hallway with a bar over my shoulder and he yelling at me to not quit if I even thought to hesitate in my steps. We drew a few spectators and at the end of the hallway he finally allows that I can get up. I try to stand and cannot. My quads just don't have and juice and I collapse against the wall in the corner and slide to the floor and tell him that I hate him on the way down. The owner of the gym was watching this and said he hates him too. Everyone laughed.
After it was all said and done and I had managed this journey down the hallway 3 times he told me that only a precious few of his clients could ever do that and I confessed to him how I wanted to hurt him. He laughed and asked me if I got all "Ninja" on him. He said it was good to use the anger to get the most out of an exercise. We have a pretty good understanding of each other after working together for 2 plus months. The time always flies and it is always very productive. At one point during this session he commented that he would be willing to make a trainer out of me one day. He says I have good confidence and attitude. Oh yeah it was after I had tried to stand up and collapsed for the third time and I just laid there and shook for awhile and then as I was getting up very slowly and with great care, I looked at him and asked him if that was all he had. Then I told him that he didn't scare me. He is a good 11 inches taller than me but I am sure that I am bigger. Of course it was all in fun and it always is fun.
It was a good workout and the kind of one where you feel good about spending all that money on a trainer. I can promise you that I could NEVER push myself that hard.