During my initial brief to new soldiers I explain that I'm pretty laid back and easy to work for except when I get mad. There are several things that will get me mad, making the same stupid mistake three times, putting a fellow soldier's life in danger, or telling me a lie will cause me to loose my temper. Of the new guys one will always decide to push me until I lose it just to see if I will.
There is a science to chewing someone out. Always have a third party as a witness. You start off low key, ask if there is a reason. Its the worst thing in the world to chew someone out for not making a run just to find out they have been trying to hide an injury to avoid being taken off the team. If they lie or don't have a valid excuse then you pick it up a notch, get inside their personal space and start talking just a little bit louder. You never ever degrade a soldier. Phrases like "Are you stupid?" "You're the worst soldier in the company!" are not appropriate and should not be used. If a leader degrades his followers they will eventually believe him. Instead say something to the effect of "Army standards are such-and-such, you failed to meet them." That way the soldier knows what you expect out of them and gives them a goal to work towards. On a biological level humans are social animals. Deep inside our subconscious we have a pack mentality therefore phrases like "You failed to keep up with the squad" work extremely well. You have given them a number to reach and reinforced it with the subconscious desire to run with the pack.
Once that is accomplished you back up and bring it down a notch or two. I highly recommend ending such a session on a positive note if possible. How you manage to do that I leave up to you. My 'verbal counseling' sessions are legendary. If the soldier has any kind of heart it only takes one of my 'talks' to get them on the straight and narrow and keep them there.
I've posted this random tutorial because a few days ago I had to verbally counsel one of my soldiers. I don't have kids yet, I really want kids someday, when at the grenade range, someone gets nervous, pulls the pin, slips and drops a live grenade at my feet I get just a little bit freaking livid.
People outside the range heard a scream and saw a ball of asses and elbows roll out of the building (that was me pushing the team out and tripping and rolling into the ball at the same time... and maybe screaming, I really don't know) followed by a rather loud bang and a string of cussing that would have made a sailor cover his ears. You know you did a good job when, days later, the company is talking more about the ass chewing than the grenade.