Something chaotic is really out of control or disorganized. Chaotic starts with a hard "K" sound (kay-AH-tick), but things that are chaotic are usually not OK, they're crazy disordered, like your crammed locker at the end of the school year.
Chaotic is an adjective that comes from the noun "chaos," meaning complete and total confusion or lack of order. Your teacher might find it chaotic inside the bus on the way home from a field trip, with so much talking and singing and stored up energy bouncing around. A classic example of something chaotic is the running of the bulls in Spain, an event that lets people run the streets with a bunch of huge, sharp-horned bulls. It's totally chaotic!