If it was a BGP peer who normally sends you 3 prefixes with under a /20 in aggregate and they suddenly started sending you a whole table, or if you allowed a peer to send you a default route, then both of those are highly avoidable through session configuration and filtering.
If the route which caused the madness came in via a large settlement-free peer (like a big eyeball/access network) or a transit (which is probably giving you the whole table) that's entirely another story.
That wasn't my point though. If you normally take 3 prefixes and suddenly you are receiving 800k+ prefixes then that likely classifies as "unexpected" (and avoidable since you can define max prefixes accepted per session).
I wasn't suggesting you could, I was questioning whether you should. :-)
If the route which caused the madness came in via a large settlement-free peer (like a big eyeball/access network) or a transit (which is probably giving you the whole table) that's entirely another story.