Reserved, diligent "a-lot-has-happened-since-I-became-a-teacher" Sawa-chan's facade cracks in S2 E10 "Sensei" when people start calling Death Devil "cute" during the wedding performance. She snaps hard enough that the lights in the auditorium go out.
The first time My love is a Stapler is played on stage. Yui forgets to sing. Mio jumps in to take the words. For the shy girl she is, that's pretty awesome.
Then they turn it into a pretty epic duet.
The seiyuu actually playing their instruments for My Love Is A Stapler and Fuwa Fuwa Time in the Let's Go concert.
And in the Come With Me concert, Pure Pure Heart and U&I (as well as performing Fuwa Fuwa Time again).