Junkman
Junkman can take two forms. The first kind brings all his junk with him, and the second kind takes junk back with him.
Junkman #1 ignored you when you told him that storage space on a boat is limited. You should be grateful he didn't bring hard-sided luggage, but the two gigantic, heavy duffels are bad enough. Even worse, his stuff is strewn all over the boat, and no amount of begging will get him to stow it: those lockers in his cabin are neither big nor convenient enough for him. So, every time the boat heels, his stuff flies all over the place. Boy, it would be a real shame if his PDA got smashed...
Junkman #2 spends your entire trip haunting tacky tourist shops. It is for visitors like him that vendors set up clotheslines hung with t-shirts on what would otherwise be pristine beaches. When Junkman asks where a particularly obnoxious trinket was made, the vendor invariably tells him it was locally made ... and Junkman believes it! If Junkman's sins are compounded by him either being cheap or indecisive, your misery will be tripled, as you are forced to listen to him dither over which velvet Elvis painting he should buy.
We got tired of following our Junkman #2 around to various shops in the Caribbean, so we finally told her that San Juan airport (where she would have a long layover on her return trip) has an extensive array of fine but inexpensive shops. Sure enough, the next time we saw her, she was proudly wearing one of those fake "Polo" sweatshirts (50/50, not 100% cotton) with "Puerto Rico Polo Club" painted on it. It was made in Indonesia.
I was invited ... to cut per person costs ... on a BVI charter with a couple of friends. (The fact that they totally misrepresented their sailing skills and experience, and the fact that I ended up running the boat, is another story altogether...). This pair insisted on bringing along full scuba gear, nothwithstanding the fact that it is easily rented in the islands. I magnanimously offered to carry some of it for them, since they swore up and down that they hadn't brought weights along with all the other stuff. After wearing myself out hauling all this stuff, it turned out that NOT ONLY had they brought weights along, but they didn't dive a single time on the entire trip!