SE in slang uses
[1930s+] to affirm emphatically and without qualification.
[mid-18C+] to accept as the truth, to have complete faith in.
[late 19C+] to give up, to abandon, to renounce.
[mid-19C+] (orig. US) to make an elaborate or exaggerated oath, usu. in the face of another’s disbelief.
[2000s] (US black) a general interrogatory phr.