What are five incidents that support the two themes of "the course of true love never did run smooth" and "oh, what fools these mortals be."

Okay, some of these can work with both statements.

Egeus is outraged and wants Theseus to give Hermia the death sentence for her disobedience. Hermia likes another guy (Lysander) instead of the guy he wants her to marry (Demetrius). That's pretty harsh considering Hermia is the daughter of Theseus. I'd call that foolish and love not running smoothly.

Demetrius and Lysander bicker over who should get to marry the lovely Hermia.

Hermia's friend Helena wanders in. Helena is all dishevelled because she still loves Demetrius; she's upset that he wants to marry Hermia. Lysander and Hermia assure her that Demetrius will be single and free as soon as they elope.

This whole thing sounds pretty foolish. I can't believe they are supposed to be adults!

After Puck spills the love potion everything gets mixed up. Lysander loves Helena and so on. It gets difficult to track exactly who loves who.

I find the line "what fools these mortal's be" kind of ironic. One of the running themes here is the same silliness going on in the spirit world. Oberon and Titania bicker constantly. Oberon even makes Titania fall in love with Bottom with a donkey for a head.