I think it's 乗り, which in this case would mean "going with/getting carried by" (the rhythm, the flow...; compare with the less metaphorical 風に乗る). I think you can translate it as "it's like when you get carried away and call your teacher 'dad', huh?", or something like that.
This picture is very well drawn. Thank you for having the source.
Da?The joy of Ash-kunPhantom Brave 4-panel comic theaterIt's OK Marona, I'm not laughingBut Ash-kun was a tiny bit delightedLook, look, da...Ok, it's done!portrait, portrait...a portrait of Ash...Ah, uhmm, it's like when you call your school teacher "dad" inadvertently, right?