YSK if you're ever in a plane that crashes into water, DO NOT inflate your lifevest until you are outside the aircraft. Inflating your lifevest inside a sinking aircraft will cause you to float and become trapped.
from /r/YouShouldKnow
YSK如果你乘坐的飛機墜入水中,在你離開飛機之前不要給你的救生衣充氣。在下沉的飛機上給你的救生衣充氣會導致你漂浮並被困住。