1) Substitute for 'mate' when addressing a close friend or acquaintance. Often reserved for someone you admire for their hard work or toughness.

2) Testicles

When you have recently blown your load and are very down and tired.

injure oneself in the testicles, usually through a hard blow or landing

To be covered in semen or to be extremely tired.

the knacker man, as in "fit for the knackers" i.e. exhausted, dead

1. Derogatory and politically incorrect term for member of the Irish Traveller community.

2. Irish equivalent to someone from 'The Hood'.

Plural noun - "Knackers" is a traditional British slang word for Testicles.

The word has found occasional usage in other parts of the anglosphere.

"Knackers" is often used as an interjection to show disbelief or as a term of exasperation. The word is more or less synonymous with Bollocks - meaning something is broken, false, wrong or malfunctioning.

The word repurposes another slang term - Knackered which means tired, broken or malfunctioning.
("This gear box is getting knackered") and is instead used purely to denote testicles.

The etymology probably has its origin in attacks on the testicles; so to "Knacker" someone would be to render them incapacitated (broken), and kicking someone's testicles is a fast way to do this. So to kick someone in the "knackers" would be to put them out of action.

"Knackers" is generally regarded as slightly less offensive than "Bollocks" as a term.

The word "Knacker", can be used to describe a lone testicle.