Too large; baggy — describes clothing or footwear that is loose and oversized on the wearer.
このジャケットは私にはぶかぶかで、肩幅が合わない。
This jacket is too big for me; the shoulders don't fit.
子どもが父親の大きな靴を履くとぶかぶかになる。
When a child wears his father's big shoes, they become baggy.
ぶかぶかのズボンは動きにくくて嫌だ。
I don't like baggy pants because they're hard to move in.
Bulging; warped — describes something puffed out or distorted from its normal shape.
古い革の財布が湿気でぶかぶかに膨らんでしまった。
The old leather wallet swelled and bulged from the humidity.
床の板が濡れてぶかぶかと反っている。
The floorboards got wet and are warping and bulging.
Onomatopoeic sound like 'parp/toot/blast' — a low blowing or honking sound (used in sound-description contexts).
船の汽笛が遠くでぶかぶかと鳴った。
The ship's horn sounded far away with a low 'parp'.