It's perfectly legal to use someone-else's idea, but it is a bit of a jerk move take someones idea and walk off with it. Just be upfront about it from the begi

It's perfectly legal to use someone-else's idea, but it is a bit of a jerk move take someones idea and walk off with it. Just be upfront about it from the beginning - agree at the start of the weekend that anything (ideas or code) that is made over the weekend goes into the public domain (or alternatively everyone in the team gets a non-exclusive licence to do whatever they want with it. Alternatively find your own ideas or find a co-founder who brings equal value to the table.