Coffeelock // Cocainelock

To be a bit more specific than u/Xavius_Night ‘s (accurate and funny) answer, the Coffeelock is when you multiclass warlock and sorcerer and abuse the interaction between pact slots, font of magic, (usually but not always) Aspect of the Moon, and repeatedly short resting.

Essentially, you turn all your warlock pact magic spell slots into sorcery points, then turn those back into sorcerer spell slots. Short rest to recover the pact slots, rinse and repeat. With enough time, you can essentially amass infinite Sorcerer spell slots. It gets extra nutty when you no longer need to sleep - the Aspect of the Moon Eldritch Invocation is the most common way to achieve this. While the rest of the party is taking a long rest, you just take 8 or more consecutive short rests instead, building up huge numbers of slots.

One of the books (Xanathar’s I think?) kiiind of addresses this with an optional rule that gave exhaustion penalties for going full nights without sleeping, but this just led to the more extreme version of the build, called the Cocainelock - doing the same thing but using Greater Restoration to remove exhaustion, either through your own spell list as a Celestial Warlock (as Xavius_Night mentioned) or through another party member. It’s so named because of the costly material component of Greater Restoration… you’re constantly snorting “powdered diamonds” to keep the machine running on no sleep.

It’s funny in concept but very cheesy and most tables will find some way to shut it down if it’s being abused, even if it technically fits within RAW.

Aspect of the Moon

Source: Xanathar's Guide to Everything
Prerequisite: Pact of the Tome feature

You no longer need to sleep and can't be forced to sleep by any means. To gain the benefits of a long rest, you can spend all 8 hours doing light activity, such as reading your Book of Shadows and keeping watch.