lacking principles or scruples; "the rascally rabble"; "the tyranny of a scoundrelly aristocracy" - W M Thackaray; "the captain was set adrift by his roguish crew"
If someone has a roguish expression or manner, they look as though they are about to behave badly. She was a mature lady with dyed ginger hair and a roguish grin. someone with a roguish expression or smile looks amused, especially because they have done something slightly dishonest or wrong