Re: Banned from Aikido...
Hi, this made me laugh.
Neither "some lessons in krav maga" nor an "aikido yellow belt" will be decisive for winning a fight. So if you do/ did this street fight, the winner would have won because of sheer force, velocity, brutality, biting/ ball kicking or whatever, but not thanks to superior martial arts skills.
I wouldn't see any reason to ban someone due to a "fight for fun", but maybe there is a reason for banning in making Internet publicity for this fight and linking it to questionable aikido skills?
I'd just ignore this type of challenge, and if you're really interested in seeing how far your aikido takes you against some other's krav maga, go to MMA or similar training and see what it's worth.