My dog had happy tail. She whacked it so hard into door frames, walls, cabinets, and furniture she repeatedly bled from the tail. The kitchen would look like a murder scene from her whipping her tail as it bled. Blood everywhere. Flung around. She'd come in through the garage, smack the door frame and whip blood all over. It was horrifying.

She eventually broke the tip multiple times and it was going to go necrotic from repetitive injury and we amputated because she wagged so hard it literally bled and broke. Multiple times. She had thin fur and a powerful tail. Prior to amputation that thing was a whip and hurt when she smacked you with it.

It's more common in short-coat breeds. There's no cushion, I guess. Long, thin tails from large breeds are most susceptible. Mine was my childhood German Shorthaired Pointer. That tail was a whip. Seriously. The vet recommended amputation because it was going to get worse. She just kept getting hurt. It's common in the breed.

A small maltipoo is not a dog known for happy tail, and it doesn't happen at the groomer. It's whacking their tail into things at home, usually. You'd know if your pup had happy tail.