I'm not convinced that explaining your "lady dick" is smaller and limper than your average man dick is quite the convincing argument they might believe. "Just like the regular ones, only less useful", wouldn't make the cut if you were selling pencils, let alone pencil dicks.
That aside, the very basis of women's oppression is that men believe they have an absolute right to use and control female bodies. Men have never respected women's boundaries and rape culture is a result.
Our lesbian sisters have an absolute right to choose who they have shake hands with, let alone who they have sex with.
I am horrified that anyone, but especially men, would suggest that choosing who you have sex with is anything but a personal choice. Any ethical human being would understand that and respect those boundaries. Arguing transphobia because lesbians won't sleep with them is just old-fashioned male entitlement.