Yes, I fire them. The form backlash varies a lot depending on the customer and how I handle it. I'm rather smaller than Digital Ocean (I recently dropped below 2000 customers) so I have something of a more personal touch, which usually helps more than it ought to help.

I also strongly select for customers who have some sysadmin experience (e.g. I turned someone away this morning who wanted a VPS but didn't want to authenticate with an OpenSSH public key) which helps a lot (but also vastly decreases my customer base.)

Worst case is when someone knowledgeable setup someone else on my service, then broke off contact; I'm now expected to step in and essentially be their sysadmin for $12/month. - That's the problem with unsophisticated users in a unsupported environment; they don't know enough to know if the problem is a hardware problem (which really is my responsibility) or a configuration on their own VPS.

but yeah, occasionally I get someone really, really angry. It's no fun.

My least favorite part of the job is firing customers who are the /target/ of DDoS attacks. I mean, if the attack is smaller than my pipe, I can tolerate it, but I've had customers hit with 10 gigabit+ attacks. Few providers can deal with that, so you are forced to get rid of the customer; It's really sad and messed up, because sometimes it's not even the customer's fault. Someone on the internet who controls a botnet doesn't like them. It's not fair that you finish the job, but there often isn't a whole lot of choice in the matter.

I have a whole lot less sympathy for people who allow their domains to be compromised and used in those attacks against other people.