Pretty much any time raocow sounds the least bit sad or loses his goofy flair. This is made worse because typically it's due to him having a really tough time on something, and he beats himself up over it.
Just about all of this video is an extremely good example of this in action. Poor raocow.
R.I.P., Gaston. Also, if one listen closely, a sniffing can be heard.
This video. He just... he sounds like he feels he's disappointed everyone.
The beginning of this video. When Yanama claimed (falsely) to be dying of leukemia and said his hack "Notte Luminosa" has never received a proper Let's Play, raocow decided to LP the hack, interrupting his LP of "Drama Mistery". What a nice guy.
raocow's reaction to sucking up Eddie in the finale of Rockman 4 Minus ∞ is genuinely sad. He knows Eddie won't show up, and he even knows that he is presumably dead. Worst off isn't just the fact he sounds so dejected and depressed, but he didn't mean to, unlike most players who do so for the "reward" you gain.
The first level of this video references the death of Gaston, raocow's cat, and the second level of the video has an Easter Egg dedicated to a person who passed away.
Despite being also a Funny Moment, raocow dream-nailing the ghost of Songstress Marissa in Hollow Knight comes off as a major gut punch, and his Heel Realization later on only adds to the tragedy of essentially killing some of the last remnants of a dying kingdom.