Green’s Dictionary of Slang

bell end n.

also bell, bell ender
[the shape]

1. the tip of the penis.

[UK]Partridge DSUE (5 edn) 1079/2: The glans penis; mostly in compounds: bell-end,blunt end, red end: esp. Services’: C 20.
[UK]McConville & Shearlaw Slanguage of Sex.
[UK]J. McDonald Dict. of Obscenity etc. 10: For added vividness a bell-end is sometimes called a cheesy bell-end.
[UK]K. Sampson Awaydays 78: Alternating deep draughts which take my entire length inside her with delicate tongue jobs on my bell.
[UK]K. Sampson Powder 380: Teasing himself in the shower, deluging his numb bell-end with the scalding needles.
[UK]M. Manning Get Your Cock Out 32: Freeloaders [...] snorting lines of cocaine from each others’ naked breasts and straining bell enders.
‘Rev. of Enge Teeny-Saue’ on YourChoice.co.uk [Internet] Commuter Tonia [...] sweet talked into parking in the woods. Tongue tweaking her small, hard nipples has the desired effect; her lips wrapped ’round his knob [...] his spunk spurting into her mouth from his engorged, purple bell end.
[UK](con. 1980s) I. Welsh Skagboys 84: Ah kin still git the bell-end n even a bit ay the shaft on a good day.
[UK]I. Welsh Decent Ride 279: A strand of pre-cum hanging from bottom lip to the bell end of Terry’s cock.

2. thus, a general term of abuse.

rec.sport.soccer (Usenet) 28 Sept. [Internet] Perhaps you are referring ot that infamous collection of bellends known as w.b.a. (win bugger all.
[UK]K. Sampson Awaydays 33: Them bell-ends. Been caning it down.
OnLine Dict. of Playground Sl. [Internet] bell-end n. [...] 2. An excessively stupid or unpleasant person. [Ibid.] bell-ender n. A wanker.
[UK]T. Black Gutted 40: Simon Cowell tearing into some utterly deluded bell-end of about sixteen.
[UK]K. Sampson Killing Pool 279: Let the pair of bell-ends tear lumps out of each other, far as I’m concerned.
Huffington Post 27 Aug. [Internet] You’re [i.e. Donald trump] a bellend mate.

In derivatives

bellendery (n.)

stupid behaviour.

Twitter 28 June [Internet] Who do we complain to about ‘official’ bellendery at Wimbledon please?
[UK]Guardian CiF 21 Aug. [Internet] Arrogant bellendery seems to be common feature amongst the Alumni of Fettes College.