Ask HN: My cofounder is freaking out about getting sued.

I have a serious problem with my co-founder and I’m not sure how to handle it. We just launched a more complete version {1} of the popular Yo App and we are getting lots of downloads. But now, he is freaking out about getting sued for using a similar name and layout as the Yo app. Mostly he is worried about having Yo in the app title, which I don’t see any problem with. However, now he changed the app title in our play store account a second time without telling me so in response, I blocked his access.

His main argument for not using Yo in our name, is that we shouldn’t be gaining traction from what others have built. However, I think tries to make up arguments why we should change the name. Also, in my opinion our app is significantly different to Yo and he is simply getting worked up about us getting sued for copyright infringement or intellectual property theft.

Moreover, having yo in the name is crucial for our app to gain traction as it communicates to people that they can do “one-word” communication to their friends similar to Yo, just in a bit of a different way.

I think my question is, is there any way we could get sued realistically? The thing is that we’re in German jurisdiction, so there is not much anyone can sue us about outside of Germany and if it goes through, it would take a year or so, wouldn’t it?

{1} https://play.google.com/store/apps/details?id=com.messenger.labs