While I generally hold tightly to a lawfully good style of play, an exception I make is stealing something to provoke the owner to send thugs after me. I'll usually only try this with such folk as the Thieves' Guild, not with genuinely decent NPCs.

My question is: how do I actually get this all to happen? Does the stolen item need to be of a relatively high value? My last time in the Flagon, I nicked a bottle of mead on my way out, hoping to wake up to a fight in a few days, but nada so far. I was in sneak mode and no one saw me five-finger the mead, though I understand that neither of those are supposed to matter.

Do I need to be more patient, need to grab something pricier, or just give it another go in the event that there is no guarantee thugs will be sent after me, and it's a crap shoot every time...?

I once stole an apple, and apparently, that's all that is needed to trigger them.

Hm. Maybe I'm not stealing healthy enough items...?

If you steal the Witch Anise's book, Song of the Alchemist (which isn't actually marked as an owned items with the red lettering). She will send thugs after you, at least she has sent them after me every time.

Pickpocketing the briar heart out of a Forsworn Briar Heart is enough to invoke the thug squad.

Note that pickpocketing the briar heart out of a Forsworn Briar Heart makes them instantly keel over dead.

Interestingly enough, in the event that you have already killed Anise and proceeded to steal something from her shack, Moira (see: A Night to Remember) may dispatch hired thugs to eliminate you.

It's pretty random. I can go game weeks & not have any thugs, no matter if steal one item or twenty in that time.

Oh yes, I've gotten that note off the dead thugs before, the first time I did I was thinking..."Did Anise somehow reach out from the grave and give her "sister" a visit?" Anise had died while I was on my way back to Riverwood from Bleak Falls Barrow. She was killed by the wandering bandits troupe Chief, 2 bandits and one cowardly bandit.

Rent a room in the Winking Skeever. After the innkeeper leaves, take a boile creme tart/pastry from the tray.

Innkeeper sent thugs after me over THAT!

It's not the value of the item, it's the principle that counts.

I remember starting a Thief character, and entering the Riverwood Trader from the other door(directly leading to the bedroom), and steal their clothes to get rid of my rags.

Stole some more stuff. Then, I'm chopping wood and looking for Hod. Lo and behold, 3 guys cladded in iron armor are entering Riverwood.

you know there is a charge just to open the fridge LOL

Alvor has sent goons to get me after taking his iron ingots...funny thing was they attacked me days later right in front of his forge and after looting and reading the contract, I glanced over at Alvor thinking "oh really...it doesn't matter if they kill me huh?"