Why is HRE so annoying? From Polish point of view....

Hell... i've played dozens of campaigns with Poland, and i never managed to maintain peace with the HRE. They break all the alliances, don't respect even a marriage alliance. Once i leave one of my western towns unprotected by a larger force they invade.
Even if we didn't fight for decades they still attack. Even if they are at war with Danemark, France, Milan, Venice, they still attack me if they get the chance.
I never had such problems with f.ex. Hungary.
Even if they have stacks full of peasants the HRE still attacks my lands full of cavalry. It's like the HRE was programmed on destroying Poland :/

i agree. as holy roman empire will become the future germany, i can't help thinking that fascism has been there from the very start.(no offense to Germans)

(no offense to Germans) Yeah... me too...

i just think that the game makers applied some hidden faction relations based upon real history events like f.ex. Venice - Byzantines, HRE - Poland...

I'm not sure... Why else would we see the rather common invasion of England by Portugal or of the Netherlands (Bruges and Antwerp) by Scotland ? Or Milan reaching up to Bern and Metz ?

I think it is rather a question of the player's faction standing and diplomatic reliability, as well as overall strength...

Once your power is rated as supreme, you do not encounter as much unwarranted attacks..

There are some default values set about faction relations. Check it in descr_strat file.

Yes. The descr_strat file does have relationships between nations. The relation for HRE - Poland is -0.2 which is bad but not enough to attack you every turn they get. Unless you've tampered with the descr_strat file, I don't know what to tell you.