Answer: Allan
The name "Allan" had to be changed to the name "Theodore", as it was Armpit who said it in the movie. The line above is taken directly from the book. It was said at the end when Stanley and Zero was reunited with the rest of D-tent after their stay at God's Thumb. Apparently Armpit had learned his lesson and was feeling remorse for what he had done, which we never found out what was.
Actually, neither the book nor the movie told us what Squid, Armpit, X-ray or Zigzag did. We were only told that Stanly was accused of stealing shoes, Zero stole shoes from a Payless, Magnet stole a puppy and Twitch stole a car.
Not much have we been told about the D-tent boys' pasts but we do know from the movie that Squid's mother was drinking and his father had left them.