Comedically covered by Fred Hembeck, Fantastic Four Roast #1 informally commemorated the 20th anniversary of Fantastic Four #1 (Nov. 1961).
Numerous heroes attended the event, with Hulk, Dr. Strange, Nighthawk, Gargoyle, Hellcat, Daimon Hellstrom, and Valkyrie (with Aragorn) arriving together as Defenders.
Iceman and Angel understandably arrived with their former teammates in the X-Men. Yet when time came to roast the Fantastic Four, those two mutants got up and assembled with the Avengers.
Unlike Quicksilver (who arrived with the Inhumans but roasted with the Avengers), neither Iceman nor Angel had ever been Avengers. Reluctant to chalk this up as an in-joke or flat-out oversight, I've long suspected that Iceman and Angel initially were intended to join in Avengers #211.
The Defenders, incidentally, did not stand up as a group to roast the Fantastic Four, but Dr. Strange and Hulk were among the many heroes to make individual speeches.