midclegs - Is your friend's disbelief because he thinks that all transwomen are "Homosexual Transsexuals" (HSTS), ie. attracted to men, when in fact the vast majority are attracted to women? This seems to be quite a common misconception.
A few Cotton Ceiling videos from different perspectives - there are many more on YouTube:
The Cotton Ceiling by Gender Critiques
"A brief introduction on what the cotton ceiling is."
More on This Creepy Cotton Ceiling Business by terri strange
(Lesbian petitioning against the 2012 Cotton Ceiling workshops for transwomen wanting, according to the organiser, "to get laid")
The Cotton Ceiling and bigotry against sexual orientations by Kizzume
( terfisaslur.com/cotton-ceiling/ )
The Cotton Ceiling: A Post Modern Affront to Lesbianism by Magdalen Burns
"Simple critique the "cotton ceiling" is a term coined by creepy porn star Drew DeVeaux which rationalises coercively guilt tripping lesbians into sex with penis-bearers."
RE: "I'm Transphobic Because I Like Boobs & Vagina" by Magdalen Burns
"Magdalen Berns responds to Arielle Scarcella’s diplomatic question "Where do we draw the line when it comes to respect for ones sexuality and respect for ones gender?" with a critical perspective on the "cotton ceiling" (the claim that lesbians who refuse to validate the gender identity of heterosexual MtT people, by pretending not to be lesbians, are "transphobic") and the antithetical relationship between the LG (i.e. homosexuals) and QT ("queer"/"questioning" and transgender) "liberation" movements."
RE: "Are genital preferences transphobic?" Give it up, Riley! by Magdalen Burns
"Riley thinks "the answer is more complicated than you might think". Magdalen has heard the line #TheresMoreToItThanThat many times before and isn't buying what Riley is selling either..."
Protect Lesbians From Men Who Claim to Be Lesbians by Erin Brewer
"Trans activists not only insist they are women, they also insist they can be lesbians. They want to break through the "cotton ceiling" and insist that a lesbian who does't want to have sex with a trans woman is transphobic. Trans allies are trying to take over women's safe spaces, and threatening violence against anyone who objects. We need to stand up to these bullies."
Trans Women and Radfems/ Terfs by Spooky Rad Luka
"rape and sexual abuse/cotton ceiling mention"
(Rad Fem Transman reads and comments on script by friend who is a 'dysphoric biological male' about the cotton ceiling - both have been called "TERFs" and "transphobes" by trans activists)
What is the Cotton Ceiling - Angela Wild #GetTheLOut - Filia 2019
LESBIANS AT GROUND ZERO: LESBIANS AND THE COTTON CEILING
A number of transactivists on social media have shared the view that they are discriminated against because some lesbians refuse to have sex with them, propagating the idea that lesbianism is “transphobic”. Get The L out Lesbian activist group investigated this phenomenon called the “cotton ceiling” and published in March 2019 a research showing that lesbians are under huge pressure within LGBT communities to accept without question that “transwoman are women”, with implications for lesbians to be able to name themselves lesbians and lead a lesbian life.
This talk details the findings of the research and discuss the political implications of these findings for lesbians, L/GBT groups, charities and organisation and women-only spaces.
This talk was recorded at Filia conference in Bradford on the 19/10/2019
It's Ok to exclude dick from lesbianism by Pippa Fleming
Consent and Cotton Ceilings Mike Harlow
(Gay man explains how he politely rejected sexual advances by a transman and then a transwoman criticised him for his "sexual choice")
(That last one can't be the only one from the perspective of a gay man as I have come across videos by transmen and detrans women demonstrating that gay men are being similarly harassed. For gay men though it seems to be just at a personal level, rather than a "takeover" of gay spaces.)