Charlamagne tha God is catching major heat from the transgender community after a guest on his radio show joked about killing transgender women -- and the backlash started during his appearance at Politicon.

Charlamagne was speaking Sunday at the event in Pasadena when advocates for transgender people began shouting at him ... "We are not a joke! Trans people are not a joke!" 

The outrage began building last week when comedian Lil Duval was on "The Breakfast Club" ... and said if he ever discovered he'd unknowingly slept with a transgender woman, that woman would be "dying." 

After Duval made the remark, Charlamagne, DJ Envy and Angela Yee seemed to condemn it, saying that would be a hate crime.

Nonetheless, some folks wanted a strong reaction ... rebuking Duvall's violent hypothetical notion. Now there's a push on social media for a boycott of "The Breakfast Club."