I love the epithets attributed to some of the major players at the center of the chaotic game of thrones that was Norman England.*
and my personal favorite
What would yours have been?
So we did some family history research, via the records of a famous ancestor (Granville Sharp the abolitionist who is my great xN uncle). We discovered we can trace out ancestry back to the Richard “Scoundrel” Greenville. Which is pretty cool IMO. Apparently he got the epithet because he changed sides so often during the civil war*, and at one point took it upon himself to lead a bid for Cornish independence…
Never mind being remembered for great deeds. There is something cool about being remembered through the ages as a complete bastard 
‘*’ - which technically makes it an early modern epithet not a medieval one.
If you are sticking to actual medieval epithets it’s hard to beat the vikings…
Ivar the Boneless
Eric Bloodaxe
Harald Bluetooth (so named for always lending mobile phone accessories to a friend who needed one )
Bertha Broadfoot
Mother of Charlemagne by Pepin the Short
BTW, Æthelred’s epithet “Unready” does not mean “unprepared”, but rather “given poor advice”. It’s a pun on his actual name Æthelræd, which means “noble advice” or “good advice”.
But only if they were close by. Distant friends were just out of luck.
I presume you’re aware of this, but the wireless protocol is actually named after Harald Bluetooth, because one of the project founders had recently read a historical novel or something.
My favorite is Ivaylo the Cabbage.
He even has an awesome statue.
He was nicknamed Bardokva (“radish” or “lettuce” in Bulgarian) and Lakhanas (Λαχανᾶς, “cabbage”) in Greek.
Yeah I think because of the Scandinavian connection with companies like Nokia.
The following are listed among Viking names:
Ulf the Squint-Eyed
Eirik Ale-Lover
Eystein Foul-Fart
Ragnar Shaggy-Trousers
Kolbein Butter-Penis
Herjólfr Shriveled Testicle
Skagi the Ruler of Shit.
A few more:
Audun Thin-Hair
Gunnstein Berserks’-Killer
Herjolf Bent-Arse
Audun Thorolfsson the Rotten
Eystein Foul-Fart
Asbjorn Muscle of Orrastead
Thorir the Troll-Burster
Thurid the Sound-Filler (I’m guessing she was a loquacious woman.)
Thorbjorg Ship-Breast
Ljot the Unwashed
A little further east we have Constantine V of Byzantium, who had the misfortune to soil the font at his baptism and was known ever after as Constantine Copronymus, or Constantine the Pisser.
ETA: Sorry, not English. But still interesting.
Don’t forget his less accomplished brother, Æthelwill the Unwilling.
You’re cleaning it up a bit. Greek kopros means “dung” or “shit”, as I know from too many combinatorial forms. His nickname means “named after dung”, not “pisser”
Constatine Crapper
Hairy Hari
IIRC it had something to do with Harald having big get togethers where everyone shared.