least:

• grumpy, unselfaware old men who don't take instruction and blame everyone but themselves for problems (often prone to angry, violent outbursts at self service)
• middle aged women who turn minor problems (e.g. the unavailability of a product, the length of a queue) into problems that require calling for the store manager
• the very-minor-problem-phonecallers (e.g. "i found a pit in my packet of unpitted dates - i'll bring it in next tuesday to show you")
• anyone who assumes they're entitled to something for free/cheaper just because they want it for free/cheaper (e.g. "this pear is bruised, can I have it for free?", "this is the last one on the shelf, can I have it cheaper?")
• young bogans who regularly use self service, but refuse to learn how they work, resulting in numerous errors and then give me dirty looks (or no looks at all) when I repeatedly fix the errors and explain how to stop the errors from happening
• the serial no-apparent-reason-refunders (e.g. "I bought these chips and dog food a week ago, but I don't want them any more")
• the I'm-not-going-to-acknowledge-you-with-a-smile-or-a-hello-through-this-whole-trolley-load-transaction-ers
• customers who stand bored in a queue with their full baskets on the conveyer belt and refuse to unpack them
• customers who wax lyrical about how much they hate self service, while using self service

most:

• little old men and women who are nervous but eager to learn how to use self service and feel good about themselves when they can do it
• old men who seem to get a lot of enjoyment out of giving compliments (esp. about my lipstick)
• kids whose parents send them in to get things while they sit in the car having a ciggie
• middle aged bogan women who address you as "darlin", "sweetie", "love", "honey", etc. when they ask for their longbeach original 40's
• good, conversational housewives
• flirty mid-20 year old men who try really hard to make conversation
• old men who reply to "how was your day?" with "fantastic" or "excellent" or "wonderful" and tell you that every day you're alive is a great day