In a previous post, Mr Giannopoulos said he wore the pin "to represent my gratitude for the LGBTQ community" and brought the fan "to celebrate the joy and freedom of gender nonconformity".
"Taking pride in queer identity means rejecting the shame imposed upon us by a harsh society," he wrote.
"It means opening yourself up to a lifetime of criticism and misunderstanding, but knowing that it's worth it to be able to live authentically."
Mr Giannopoulos is a special-education teacher at the Beacon Charter High School for the Arts in Woonsocket, according to the Rhode Island Department of Education.
Trump met with Teacher of the Year winners on April 26 at their traditional White House visit.
- news.com.au