I have a friend who has a habit of joking about being an apikorus (because he wears his peyos behind his ears). Beyond the strictly judgmental, is there a problem with self-referencing as an apikorus, particularly if one is known to be fromm (religious) and to believe in the ikarim?
I think that there is a general prohibition that one is not allowed to be self-disparaging. I haven't seen this as an actual issur - prohibition per se. However, there are many paragraphs in Pirkei Avot that in some way, mention that one should not do this. The two most notable that I can think of:
וְאַל תְּהִי רָשָׁע בִּפְנֵי עַצְמָךְ - Avot 2:13
Do not be a wicked person in your own eyes.
אל תהי בז לכל אדם - Avot 4:3
Do not disparage anyone (i.e. - including yourself. It does not say "anyone else")
An apikoros, as you know, does not receive commendations in the Talmud, or anywhere, in general, in Judaism. Self-evaluation is valuable if it is used to improve oneself. But, generally, a person should not publicize his own character faults other than for useful positive purposes. For example, if he had a flaw in the past that he has improved, it is very useful to teach others who have currently a similar flaw, his example of how he improved himself so that they learn to emulate how he improved.