Lindsay Lohan -- Bad Head for Business ... Allegedly Jacking Idea Could Cost Her Millions

Lindsay Lohan -- Bad Head for Business ... Allegedly Jacking Idea Could Cost Her Millions, Lindsay Lohan got in bed with a website developer, fell in love with his idea ... and then screwed him -- the bad way -- by taking his idea to someone else ... according to the developer who's now suing her and her brother.

Fima Potik says Lindsay and her bro Michael Lohan Jr. agreed to work with him on Spotted Friend -- a website that gives people a chance to see the clothes in celeb's closets ... according to his lawsuit.

But Potik says LiLo and MiLo Jr. backed out and took his idea to another investor. He says he got a text from Michael Jr. saying he wanted a bigger cut of the company, or else.

In the suit, Potik says Lindsay and Michael went off and started an app called Vigme ... which he describes as a carbon copy of Spotted Friend. So, he's suing them in NY State to get Vigme shut down. He also wants a ton of cash -- more than $60 MILLION!