If you need to defend yourself against an aikidoka, like mentioned above, it's quite likely that you pushed too far... Unless the technique was done with intent to do serious harm, maybe you could simply blend with it, take ukemi, and apologize, right?
Of course, if you're attacked by any of the aikidokas I know (including me), the best defence would be to distract them with beer or pizza... Cookies might work too...
Joezer (who, by the way, really likes extra peperoni on his pizza, thankyouverymuch