Complex sentence: The song is about a man who gets exaggeratedly depressed when drinking other soft drinks, like for example, Sweet Success would fail him and Samuel Adams Lager would make him ill, but he gets happy when he starts drinking Pepsi.
Split into simpler sentences: The song is about a man who is gleeful thinking about Pepsi, but gets exaggeratedly depressed with other soft drinks. For example, Sweet Success would fail him and Samuel Adams lager would make him "ale", but he gets happy when he starts drinking Pepsi.