While smoking Marijuana communally among a group, a bottlenecker is an individual, when passed, keeps smoking the joint/spliff much longer than they should resulting in others frequently reminding them to pass the joint/spliff to the next recipient.

The individual effectively creates a bottle neck in the flow of weed being consumed within the group.

Computer-related definition: A part of your computer internals is slowing your entire system down.

A bottleneck is a point of congestion in a production system (such as an assembly line or a computer network) that occurs when workloads arrive too quickly for the production process to handle.

A co-worker who takes so long to do their job they make every project take longer than it should.

when you stick your flaccid penis in a bottle then make it go erect inside the bottle

When something or someone in your life just does not allow you to succeed.

Removing the cap of a beer bottle in one's anus while using said beer bottle for anal stimulation.