To be tongue in cheek means to be humorous / to consider something or what somebody said in a funny way and not seriously.
1. The Webmaster made a tongue-in-cheek comment about the referral bonus for members.
2. Tongue in cheek, the teacher said that naughty Pratik should get an award.
3. Although Shirin sometimes sounded rude, the people who knew her closely always took her words tongue in cheek.