I heard one doesn't need an AOC for joy flights
I was going to post something along the lines of "even if the regs on privileges of a PPL don't get you, the requirement for an AOC might", but it seems our illustrious moderator beat me to the punch.
You don't need an AOC for joy flights, if by joy flight you mean taking friends up in your privately owned plane. As soon as you start advertising and charging, it's a commercial op.
Regardless of whether there is a loophole in the regs, you should consider the ethics of what you propose. Even if you don't make money from it as a pilot, a paying passenger who has been promised a service via advertising is entitled to regulatory oversight for their protection and safety. The regulator achieves this by issuing an AOC and certifying pilots to commercial standard. If you have not demonstrated those standards, then is it appropriate for you to offer a service?