They

• laugh at stupid jokes, accepting a low standard of conversation.
• tell stupid jokes.
• are slow to catch on to things that are being said, and once they do they don't just keep quiet, they say 'oooooh' every two minutes.
• ask you to repeat what you said. Again. (A keen observer would realize that they're not getting this particular point and just let it go.)
• understand about 30% of what you said, but insist on having the remainder explained in every little detail.
• hang on to some little expression you used and when you explain it in different words [to give an equivalent statement], they still make you explain the expression.
• constantly mix languages in a conversation for no reason (because they need/want an expression they often use).
• switch languages in a conversation for no reason.
• make what they think is a witty comment that makes no sense at all to the context and when called on it insist that 'it was a joke, lighten up'. [this one seems to proliferate lately]
• try to make you laugh and when failing accuse you of not having a sense of humor.
• are so loud you can't not hear them in the other room if you try.
• engage you in conversations about the most pointless issues.
• have their own 'signature expressions' that they insist on using in just about every sentence.
• use common expressions, incorrectly.
• completely dominate conversations, even those involving a group of people.