The Shepherd Book says the following ( chapter 5 pp65-66
16. Apostasy: Apostasy is a standing away from true worship, a falling away, defection, rebellion, abandonment. It includes the following:
• Celebrating false religious holidays: (Ex. 32:4-6; Jer. 7:16-19) Not all holidays directly involve false religion and require judicial action.
• Participation in inter faith activities: (2 Cor. 6:14, 15,17,18) Apostate acts include bowing before altars and images and sharing in false religious songs and prayers.—Rev. 18:2, 4.
• Deliberately spreading teachings contrary to Bible truth as taught by Jehovah's Witnesses: (Acts 21:21, ftn.; 2 John 7, 9, 10) Any with sincere doubts should be helped. Firm, loving counsel should be given. (2 Tim. 2:16-19, 23-26; Jude 22, 23) If one obstinately is speaking about or deliberately spreading false teachings, this may be or may lead to apostasy. If there is no response after a first and a second admonition, a judicial committee should be formed. -Titus 3:10, 11; w89 10/1 p. 19; w86 4/1 pp. 30,31 ;w86 3/15 p. 15.
Strictly speaking you cannot be DF'ed for having doubts. Of course it's not unknown. The problem comes if you start talking about those doubts as even minor conversations can be used against you.
Note the catch all "deliberately spreading teachings contrary to Bible truth as taught by Jehovah's Witnesses". This means that whatever the current view as dispensed by the GB is forms the "truth". If there is a change one day to the next then you better step into line. If you express reservations on a subject then you can be accused of apostasy.
The label is used to demonise and control people. Being a wife beater is less reprehensible than being thrown out just because you can't get your head around some teaching. Criticising the organisation is an absolute no-no and counts as much as apostasy as disagreeing with doctrine.
The attitude is optimised on JWTalk. Anyone who expresses a liberal or cautious view on a matter risks being flamed, knocked down or banned. Comments of even moderate criticism are swiftly jumped on. Many on here who have tried to make comment on matters have been quickly banned.