An "assumed attitude" is an outward appearance that may not necessarily reflect a person's true thoughts or feelings. There are many synonyms for this expression, including affected demeanor, feigned posture, self-conscious bearing, and insincere comportment. Other options might include artificial mannerisms, pretense, or even dissembling or dissimulation. Ultimately, any of these phrases could be used to convey a similar sense of behavior that is not necessarily authentic or genuine. It's important to choose the right word in order to most accurately convey the intended meaning of the phrase, and to avoid any potential for confusion or misinterpretation.