off the top of my head

to name a few:
1. underlying 140 denied if you file concurrently or semi-concurrently

2. non-immigrant status gaps before aos

3. true color Bolshevik who refuse to compromise

4. arrested and subjected to a sentence more than a year or stay in jail/prison for more than 6 months.

5. hiv positive and no relatives in america

6. fail to provide supporting documents or respond to rfe/noid

7.fraud----for this, you will be deported even after you become citizen

......