Use the adjective aberrant to describe unusual conduct. Sitting in a bathtub and singing show tunes all day long might be considered aberrant behavior.
For conduct that departs from the norm, aberrant is at hand to describe it if you want to set a formal, or even scientific tone to the discussion. You can put the accent on either the first syllable (AB-er-ent) or the second (uh-BER-ent); both pronunciations are acceptable. The Latin root aberrare means "to go astray," from the prefix ab- "off, away" plus errare "to wander." Other descendants of errare in English, like error and errant, have that double -r- and also refer to something that's either not wanted or not expected.