Chewbacca woke up one morning on the Millenium Falcon feeling a little worse for wear. He'd gone out drinking with Han in a nearby cantina they'd found shortly after landing on this planet. It'd not taken Han long to end up passed out under the table and Chewie had vague memories that he'd gone up against a local in a drinking contest. Whether he'd won or not he couldn't remember, but it was a fair bet that the usual "Let the wookie win" rule would have come into effect - a drunk wookie being a far more dangerous entity to piss off than normal.
Aside from his pounding hangover, Chewbacca soon noticed he had another issue. A series of strange itching feelings all about his body. The worst of these was right between his hairy buttcheeks and no amount of scrubbing with Han's toothbrush was helping alleviate the problem.
So he went and found a medi-droid to see if it could identify the source. After a series of tests, the medi-droid had soon spotted what the issue was. "Ewoks," it said.
"Gurrahggh?" asked Chewie.
"Yes, Ewoks. Irritating little bastards - you've got an infestation of them in your fur."
The medi-droid pulled over a display unit, "You can see them on this. " The display showed what looked like a forest of branchless trees with a dozen Ewoks trying to build a hut. Chewie absent mindedly scratched one of the itches and on the screen a giant finger came down and destroyed the structure whilst sending the Ewoks flying in several directions. At least one was squashed into a goey red paste and the surviving Ewoks shook their spears at the retreating finger. Chewbacca had the decency to look a little sheepish.
"There isn't really much you can do except...well...there's this spray I can sell you. It'll get rid of them all in one go if you cover yourself in the stuff."
Chewbacca reluctantly paid for the spray and went back to the Millenium Falcon. Once alone in his room he began spraying himself all over paying extra special attention to his furry buttcrack. The noise of the spray was louder than he expected and sounded like a million voices crying out in terror. The sound and the chill on his most tender parts causing him to pop a boner were unwelcome distractions, but he persevered as he knew if he stopped there was a chance he might have missed one. And then suddenly the cries he could hear were suddenly silenced and all he could hear was the hiss of the spray.
Deciding that he was done and that having wasted most of the day on this matter, it was probably a good idea to drown his memories of it in booze. So he went out to see if he could find Han about. It didn't take him long - Han was in the galley, toothbrush in mouth and cleaning his teeth. "Hey furball, what's up with you? " Han asked.
Chewie just grinned and shrugged. For no readily apparent reason to Han, he insisted they went to a different cantina where they both got totally shitfaced together again.