Legal Question in Discrimination Law in District of Columbia

To be protected under the Americans with Disabilities act, you need to be "disabled," or at least perceived by your employer to be disabled. Under the law, this requires that you be substantially limited in a major life activity (but still able to perform your job with or without an accommodation). So your sickness must amount to a disability (or at least be perceived by him to be a disability). With the facts as you described, it does not sound like you would qualify as disabled -- therefore, penalizing you for calling in sick would not violate the ADA.

If he is treating you differently than another employee, you may have a claim for some other form of discrimination under federal law. If the other employee is in a different protected group (e.g., a different race, gender, religion, national origin, or if you are 40 or over and the other employee is younger than you), and you are "similarly situated" (performing similar functions) and he is treating you differently because of that difference, this would be a violation of federal anti-discrimination laws. I don't know if DC protects sexual orientation, but if so, and this is the basis for treating you differently, then it may violate DC law as well.

Basically, if he's simply being a jerk, or has a personal disliking for you for some reason other than being in a protected category (disabled/race/gender/etc.) he is not violating any laws.