Usage and meaning of "占我的便宜"
"占我的便宜" and "吃豆腐" are all disadvantages for usage with nagetive meaning for daily Chinese people.

However, the first set phrase is NOT ONLY used to women but to other things as well. We usually use this phrase to describe a senario that someones (tries to) gain sth at the expense of others, but the expense is very little for the others. And the fixed one is very similar to "揩油"(ShangHai dialect).——This is very similar to you.

Another meaning is that “贪小”（greedy for small gains or profits）

Now let's see some Chinese samples:

不要捡地上随便掉落的元宝、金银器物，不要占便宜，否则你极可能被犯罪分子要挟勒索！

"吃豆腐" is used when a man wanna do something ugh to a woman (especially something that is dirty)：(e.g), A man in the bus is rubbing the woman with the reason that the bus is fully crowded with people.

For more, you can see this sample.