offhanded

"his ad-lib comments showed poor judgment"
"an extemporaneous piano recital"
"an extemporary lecture"
"an extempore skit"
"an impromptu speech"
"offhand excuses"
"trying to sound offhanded and reassuring"
"an off-the-cuff toast"
"a few unrehearsed comments"

"an offhand manner"
"she treated most men with offhand contempt"

"couldn't give the figures offhand"
"we decided offhand to go to Canada"
"she had made these remarks offhandedly"

"replied offhand, his mind a million miles away"
"she threw him over offhandedly without even a Dear-John letter"