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.
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 Infinity 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.