Re: Beginners with delusions of grandeur...
The head instructor is ultimately responsible for the conduct of his/her students in the dojo. However, sensei is busy and sometimes not always capable of watching everyone all of the time. A responsibility of senpai in the dojo is to police the actions of kohai. A beginner in aikido is by definition a kohai to those already training. If senpai choose not to tolerate inappropriate actions, this helps alleviate pressure for sensei to intervene in all but those issues that transcend the senpai/kohai relationship. Be careful to recognize the difference between approaching your instructor with a problem that you cannot resolve individually, and approaching your instructor with a problem for which you do not want repsonibility.
It seems that we as an American society are constantly looking to externalize responsibility. Take the genius that cuts off his foot mowing the lawn, then sues the lawnmower manufacturer for failing to identify the lawn mower uses moving blades that may be sharp; a jury then supports the claim saying, "well, he needs the money and the lawnmower manufacturer is so big..." We externalize responsibility and our society supports those decisions.
So what does that mean? That means that sometimes students choose not to take responsibility for issues within the dojo. How often do you hear (or think) "This guy is a jerk, and he might hurt someone BUT I don't want to get involved...", "My partner is doing the technique wrong, BUT sensei will correct him...", "This guy is fighting me and he is going to get hurt BUT I'll just change my technique to accomodate him and avoid the issue."
Ask yourself, why was I unable to correct this problem independently? Here are a couple of sources for why kohai feel they have authority to conflict with other students:
1. Ignorance. Kohain that do not realize the consequences of their actions often contest or resist senior students.
2. Respect. Kohai that do not respect senpai will often openly contradict or contest senior students in training.
3. Skill. Kohai that feel they are better than senpai will often resist or contest technique from senior students.
4. Endorsement. Kohai that feel their actions are endorsed by other students (or the instructor) will often contest senior students.