Asking for a friend…

An angel investor in a successful startup wants to cash out a bit in a secondary but the founders are telling him he can only cash out fully or stay in full. No partial sale allowed. But his shareholder docs show he has tag along rights to the tune of 20%. Would it rub off a founder the wrong way if the angel were to invoke that right? Presumably because the founder may then have to offer a partial sale to all exiting shareholders, some of whom may not have been aware of their tag along rights.