I just watched a compilation of Costa's antics on Youtube. I knew he was a tough, dirty player, but there's footage of him gobbing two big mouthfuls of spit into his hand and then flinging it at other players. What a scummy, dirty *******.
He's no angel obviously but what people fail to take in to account is the treatment he constantly gets too, it's definitely a tactic by some teams to wind him up hoping he will explode which is fair enough.
The one you mention was in response to Pepe putting a finger over one nostril and 'snotting' on him so if he replied in kind then that's tough.
Seamus Coleman was elbowing and prodding him for most of the 1st half when Chelsea visited Everton earlier in the season for instance yet when he laughed at his misfortune at scoring an own goal his team mates all started crying.