This article is from the Llamas & Alpacas FAQ, by Michael Shealy and William Bagwell with numerous contributions by others.
This syndrome is usually caused by bottle feeding a cria and/or fondling, playing llama games (bumping, nudging, running with, & cuddling) while a youngster.
The young llama then bonds so completely with humans that s/he thinks that humans are llamas too. As s/he grows, s/he begins to play rougher and rougher, until he becomes unmanageable and (not she here) quite dangerous. Females will develop the same bond, but their activities don't include chest-ramming and "serious" conflict, but very well may include frequent spitting at humans and a general difficulty in handling.
**CAUTION: This phenomena can become VERY serious and many times ends with the (male) llama being euthanized. Once they reach adulthood, turning back is very difficult and requires intensive training. **If you have a cria that requires bottle feeding, immediately consult an experienced llama handler for explicit instructions how to avoid BMS. -or- If you have a young animal that is "pushy" affectionate, beware. This is usually the beginning of difficult behavior and will more than likely develop into "nasty" behavior. Steps should be taken immediately to redirect any pushy behavior.