Why is it such a surprise????
It should be remembered that aviation attracts people from all walks of life - with all different attitudes and personalities.
It is nice to think that in our "professional" world people would contain sufficient situational awareness and courtesy, but just like on the road, in an accounting firm or a servo, etc, there will always be people who are selfish and feel that they are more important
If these wankers piss you off enough then write a letter to their CP mentioning what happened.
Maybe they will learn something.
Maybe they won't.
If they don't, and are naturally just selfish, then dont worry about it!!
Every dog has their day......
On a different note, if your IFR deptarting from an OCTA aerdrome you of course dont need a clearance (unless your going to Class A, then you just need it before you get there).
Many times I have been at a community airstrip and departed without a taxi call becaseu HF is having another bad day, with the intention of contacting CN once airborne. Perfectly fine, as long as you remember that without the taxi call nobody knows you have departed so if you spud it in after take off nobodys going to come looking for you.....
Eternity.