In plays like The Frogs by Aristophanes, costuming greatly contributed to the comic effect. Let's look at how the actors would have been dressed and how their costumes were indeed funny.
The base costume for actors in a comedy like The Frogs was exaggerated to start with. Actors wore body suits with extensive padding in the belly, rear end, and chest. This gave the actors a hilarious profile, and the addition of an exaggerated male organ contributed to the effect.
On top of the body suit, the slave Xanthias would have worn a simple tunic. Dionysus's garment was more elaborate, a flowing robe that identified him as Dionysus, along with boots. These garments were, however, often associated with women's dress, so that, too, would be funny to the audience.
Moreover, Dionysus wore a third layer of costume that was meant as his “Hercules” disguise. The contrast between the second and third layers would have provided another comic element as the audience would certainly have noticed the discontinuity of feminine and masculine characteristics.