I have a cousin whose visted for the summer, & she is.... *sigh* she's 4 & her name's Amiyah & guess what every time she vists she has to spends at least one 日 at my house, & she vists atleast 3-6 times a year.
あなた can just go to a different room and do what あなた do for fun and ignore him/her. Go hang out with フレンズ または do something fun at home, something that keeps the time passing faster until your cousin leaves. あなた have to be calm and don't pay attention to the annoyance. If it's hard try to listen to 音楽 and pay attention to the music/song. Turn on your fave song and pay attention to the words. If if this annoyance makes あなた angry just take a glass of ice cold water and drink it all then do something あなた do to pass time faster. That's what I do when I am annoyed and it actually works. :)