1) They make inappropriate comments ("You smell funny and why you gotta big nose?") and demonstrate their array of bodily functions at the most inopportune times, at the most public locations.
2) They have neither the ability nor desire to control the volume of their voices.
3) They do not physically need anyone present in order to engage in a conversation or argument.
4) Any little thing can make them either laugh or cry.
5) Their moods swing violently between euphoric happiness and the darkest depths of agonizing despair within fractions of a second.
6) They possess a false sense of confidence in their physical abilities. This is not helped by their spontaneity and surprising agility which fails them when it really counts. Luckily, they seem to bounce and are pretty immune from (serious) injuries.
7) People either love or hate having them around.
8) They can make or break a party.
9) They're terrible listeners.
10) They're sloppy eaters, spilly drinkers and have no concept of personal space.