A person whose conduct deviates from the conventional, giving everyone around him the creeps.
This word has its origins from the Malayalam motion picture 'Kumbalangi Nights', where the antagonist Shammi, a family-man psychopath, breaks bad at times, making the people around him uncomfortable.
Naveen: Did ya see Ravi during the presentation? He was acting all weird with those irrelevantquestions Akhil: Told ya! He's a real Shammi