Yep, I agree.
I am confident I could defend myself in most situations, but would still be reluctant to take on a young guy.
A knife or a machete brings something new into the equation and my reflexes may not be quick enough these days. I wouldn't risk it.
But take away the knife and I'd probably be ok - that is, until the police come knocking on the door to charge me with assault. No matter who is at fault in Thailand, the farang hasn't got a chance.
So I'd forgo any altercation, put it down to experience and just move on.
As paborn says, it's not worth it.
On the surface, Dusseldorf sounds attractive but I'm rather wary of guys from Eastern Europe.