Oh, I have a lot of these:
1. The Couponer
a) The Reasonable Couponer: this subtype of coupon user has a lot of coupons, is generally very friendly/sometimes chatty, and will generally accept the fact that some coupons cannot be accepted, are expired, etc. They are still a bit of a pain because their transactions are complicated and inevitably result in an "R", but they are at least courteous.
b) The Nightmare Couponer: OK, cashiers, we've all had these! They are horrible. They are retail leeches who want everything for free. Nightmare couponers are rude, pushy, entitled, and they won't take "no" for an answer. They almost always demand to see the manager, and if they still can't use all their coupons, they will typically leave all of their shit on the belt for us to put back. They hold up the line, annoying legitimate guests who actually want to pay for their stuff, and they result in an "R" always.
2. The "Wacky" Guest
These guests think they are so charming and hilarious. Usually they are young people; sometimes, it's a teenager and her parent. They sort of put on a "show" while you are checking them out. They want you to laugh at them/with them, to be dazzled by their wit and charm. Whatever you do, do not acknowledge their "humor." Be focused on your task and pretend like you are not paying attention to their half-staged conversation (unless they are addressing you directly). Note: this category does not include guests who are actually funny, only self-satisfied narcissists who THINK they are.
3. The Nutjob
These are the crazy people. They say bizarre things, have eccentric requests, ask you to do inappropriate things, steal any spare change you may have lying on the POS, talk to themselves, etc. Be friendly, and get them out of there as quickly as possible.
4. The Bagging Critic
These annoying guests come in different degrees. They may remove items you have already bagged and re-bag them, or they might give you very specific instructions on how to bag everything, as if you haven't done this a thousand times over. Sometimes they will watch you bag something and then immediately re-do it themselves. Sometimes they will say "Oh, I'm not picky!" when you ask if they want something bagged separately, but then they will "fix" everything, or they will instruct you to put everything in one bag when that is not the best way to bag the items (or even possible). They may also complain about the amount of plastic bags they have at home, as if that's somehow your doing.
5. The Protestor
This guest requires a lot of price adjustments and usually a price check or two. "Oh, no! There was a sign back there that said ....," "That was supposed to be on sale!", and "That had a price cut...." populate their vocabulary. Usually, they are looking at the wrong sign, or they didn't read a sale sign correctly. Your GSTL or GSA will usually instruct you to just "just change it." This category also includes the dreaded "That was supposed to come with a gift card!" variety.
6. The Red Flag
These guests are usually scammers. They will try to write a check with a questionable ID, pay with a fake traveler's check, or use funny-looking coupons for high amounts. These are usually (but not always) lower-income people buying expensive items (stacks of brand-name clothing, VISA giftcard, electronics) or carts full of stuff. If they really don't look like they can afford it, chances are, they can't. Note: this category can sometimes overlap with the "Nightmare Couponer."
7. The Shocked Guest
A guest buys something expensive, like a Fieldcrest comforter, and they are totally shocked by the price. Or, their card is declined, and they at like they don't understand how that could possibly have happened. They expect you to tell them what the problem with THEIR card/account is, when a payment is supposed to go through on their card, etc. All the while, they are holding up your line. Sometimes they end up leaving behind groceries they can't pay for, which always seem to include ice cream, meat, milk, and other perishables which must now be defected out. This category can sometimes overlap with "the protestor."
8. The Independent Guest
These guests act like they are checking themselves out on a self-checkout. They may be on their phones during the entire transaction; they may not even say one word to you during the process. They might be carrying on a conversation with their party during the entire transaction, without once acknowledging your presence. The good thing about this guest is that you don't really have to interact with them much. The bad thing is that it's impossible to push Red Cards.
9. The Normal Guest
Luckily, most people tend to fall in to this category. They might have a legitimate request or question, but they are not a pain to deal with. Most of them come in, load their stuff on the belt, pay for it, say "thank you," and leave.