Acid flower

The Joker commits crimes with his comedic weapons which include his famous acid-spewing flower, always tucked into his lapel. The infamous flower The Joker wears in his lapel sprays (at any given time) acid, poisonous laughing gas, water, or nothing at all. The flower's colors have varied over the years, but are usually yellow or purple.

Batman (1989 movie)

In the 1989 movie, Batman, the Joker referred to his acid flower as his 'very special flower' and removed it from his suit lapel to give to Vicki Vale. The flower looked too large and too shiny, like plastic, which Vicki noted. The Joker then squeezed the flower, which squirted out the lethal acid contained within. Vicki dodged, and the Joker later replaced the flower in his lapel. He also used it towards the end of the movie, to melt the seal holding the bell to the bell yoke in Gotham Cathedral to make the huge heavy bell plumment on Batman who was still going up the stairs, The plan failed as it just barley missed Batman only to caused massaive damage to the Cathedrals stairs. However it did, intentional or not halt the police from going up the Cathdral stairs.

Batman: The Animated Series

In Batman: The Animated Series, The Joker first used the flower in his lapel to spray laughing gas at Poison Ivy, who simply laughed, knowing that the gas would not work on her (because of her being immune to poisons), much to the Joker's surprise. She retaliated by dealing the Joker a savage karate kick. The Joker would use the flower in his lapel to spray laughing gas on his victims in several other episodes in the series.

The New Batman Adventures

In The New Batman Adventures, The Joker used the lapel flower once to spray laughing gas, and another time was able to defeat Superman with it. The Joker, during a battle with Superman, tried to use kryptonite on Superman, who had come prepared with a leaden suit. However, a dismayed Joker soon remembered the flower in his lapel. He squirted green acid from his lapel flower all over Superman, destroying his lead suit and allowing for The Joker to gleefully begin shocking him with a joy buzzer, as Superman was exposed to the kryptonite.