The phrase "getting your butt handed to you" comes from the same idea as "getting your butt kicked". The idea is that you are seriously losing to whatever is "handing you your butt" so in that context it means the intern was really REALLY having trouble keeping up with the the machine. The directions "left and right" just add emphasis so "he was getting his butt handed to him" has less intensity than "he was getting his butt handed to him left and right" If I were playing is a soccer match and my team lost by a point because the other team was a little better I might say "We got our butts handed to us" but if we lost by 4 points (it is really unusual to lose by more than a point or two in soccer) and the other team was much better than my team I would say "We were getting our butts handed to us left and right!" Note: that if you add directions you always add both opposing directions you wouldn't say "he was getting his butt handed to him left" The phrase "busting your chops" in that context means to exert yourself, usually physically. So when he said that to his instructor he means that the instructor is working really hard and "not keeping up" meant that he couldn't match his instructor's working pace. Also note that "busting someone's chops" can also mean you are annoying or criticizing someone. So if I get home really late and I accidentally wake up my mom and she gets upset and angrily starts talking to me I might say "She was really busting my chops about getting home late last night." Hope this helps! Keep learning :-)

"To get your butt handed to you" is to fail or to be reprimanded. "Left and right" means from all directions, no matter what he tried to do.

Thank you, Shawn!

Both Zahava and James answered this exactly as I would have. I'd also like to point out some other expressions that you could use. For instance, you could also say "You're really kicking ass on that machinery." This means you're doing an amazing job. Of course, this expression is informal and somewhat vulgar but so is "getting my butt/ass handed to me". lol :) You could also say "You're really slaying it on that machinery." This means that your are doing a perfect /great job at something too. "You're really owning that machinery." is another one which sounds somewhat gamerish to me. Gamers usually use the verbal expressions "to (p)own someone" when they beat the crap out of an opponent and "to (p)own it" when they completed a task perfectly, etc. :)