Unceremoniously means abruptly, and with no courtesy at all. Unceremoniously dumped, dropped unceremoniously, shown out unceremoniously.
The insult is in the abruptness — the lack of ceremony says the person was not worth any. It nearly always attaches to a verb of removing or dropping. Note the three parts: un-, ceremonious, and -ly.
1adverbunceremoniouslyAbruptly and with no courtesy.
“The drunk man was unceremoniously thrown out of the club.”
unceremoniously is a manner.
Un-, not, plus ceremonious, from Latin caerimonia, a religious rite, plus -ly.
From unceremonious + -ly or un- + ceremoniously.
Etymology from Wiktionary, CC BY-SA