kabump!, excl. — Green’s Dictionary of Slang

kabump! excl.

also kerbump

[ker- pfx + SE bump; note belly-cabump, (US) to throw oneself face-down onto a sled preparatory to sliding down a hill]

an onomat. term indicating the noisy landing of one object or person on another.

1998		‘Ginny’ ‘Preschool Songs’, Perpetual Preschool.com 2 Sept. 🌐 5 little children went to school, / 5 little children didn’t follow the rules / 5 little children jumpity, jumped, / 1 little child went KABUMP!
2001		C. Liew Pyromaniac Archive 12 Jul. 🌐 I went kerbump kerbump all the way down the stairs, and understandably when I reached the bottom I was bawling my head off. Turns out I had managed to kerbump my head rather hard on one of the walls, and received a rather nasty bruise.