now that I've written this entire megillah in rsponse to your one sentence, can someone more knowledgable than me clarify thse things?

taon

questions? go here:

1-13: various types of minim, apikorsim, and deniers of the thirteen principles of Judaism and deniers of the Torah. I saw a thread on what falls under these categories in the Basic Judaism section, here's the link:
www.frumteens.com/topic.php?topic_id=8480
14-15 denial or intentionally disreagarding any mitzvah, even one. It seems to also include avodah zarah.
16 causing the multitudes to sin. The examples given were all of people who did it purposeley, I dont know if an accident would fall under this category. I guess just watch what you say, you don't know what it may cause.
17 Seperating one's self from the community. Examples given are not joining in community fasts, not joing in their Chagim, not joining them in time sof hardship and joy, etc. I heard, but I may be wrong, that it includes not going to minyan but davening by yourself in order to seperate yourself, and possibly not following minhagei yisrael/ minhagei hamakom. If it's done becuase the community isn't frum, that's obviously a seperate story.
18 brazenly, proudly, doing aveiros in public
19-20 betraying jews to goyim, I'm not sure what this includes, it also seems to include favoring goyim, giving money that belongs to a jew to a non-jew, and more. I'm really not sure. Possibly even giving a non-jew all your business when it's about the same to bring it to a Jew. Ask your Rabbi on this one.
21 causing the community to "revere and fear you", for your honor, disregarding Kavod Shemayim
22 murder
23 loshon horah (Since the gemora says most people say l"h, it must mean frequent speakers of loshon horah, I believe)
24 someone who hides his bris "extending the foreskin" to appear uncircumsized.

there are additional ones listed seperately, whioch are less severe but if done often can be just as serious
1 creating an embarassing nickname for someone, even if they act like it's fine with them
2 calling someone by an embarassing name, even if it's so widespread it's like that person's second name and they don't care at all
3 embarassing someone in public
4 taking pride in another's embarassment
5 disgracing a Talmid Chocham (this does not apply to an apikores, or to warning someone that someone is untrustworthy)
6 disgracing your teachers (same exceptions as above, may only apply to teachers of Torah, as it's seperate from embarassing someone)
7 degrading Yom Tov. examples given are eating a lot before the chag for the purpose of being unable to eat and enjoy the yom tov meal. illlnessers and eating disorders may be exceptions, as well as obvious exceptions like not trusting the kashrus of the meal. The other example given was working on Chol Hamoed. This may or may not iclude not celebrating Chol Hamoed properly, or violating it's laws
8 profaning Kodosh things, it says by making a korban disqualified from being used and using objects set aside for kodosh use for personal use (meilah). The first obviously doesn't apply nowadays, the second may not either.
Teshuvah is always always accepted. Even in these cases. With these it may b eharder, becuase
a. it's hard to take it back
b. you may not realize it's wrong, or the neccessity of doing teshuvah for it
c. you might not do a proper teshuvah, thinking it means a lot less
d. it may seem too late to do teshuvah (never true while one is alive)
e. it may be hard to stop
f. there may be more neccessary for it to be a full teshuvah, like tzaaros from Shemayim, or your own safeguards to not do it again.