deliberately impassive in manner; "deadpan humor"; "his face remained expressionless as the verdict was read"
Deadpan humour is when you appear to be serious and are hiding the fact that you are joking or teasing someone. her natural capacity for irony and deadpan humour. sounding and looking completely serious when you are saying or doing something funny deadpan voice/expression etc (dead + pan (1900-2000))