Potpourri of old things
The Charles Atlas ads were nostalgia when the song was written. The phrase "shaking down" is used in the sense of extortion by violence - a reference to Mafia tactics of old (e.g., breaking legs), and of course it's funny to see this applied to Cupid the cherub of romance.
"Please to move your van" is the kind of joke they probably wouldn't make any more, referencing an EAASL speech pattern... today we all bristle at the slightest perceived toying (such as a cheesy accent), whether a slur is intended or no (and I detect none in this song).
"Why I'd...!" is an intentionally old-fashioned formation - like "Why I oughta...!" - which would be recognized in 1985 as an echo of many comedic performances from old movies & TV shows (and going further back, radio & vaudeville) such as The Three Stooges, The Honeymooners, and Abbot & Costello. The speaker would always be a lower-middle class character frustrated into anger, clenching both fists & grimacing. The phrase would precede a threat ("...break his legs!") but it would be understood that the threat is toothless, coming from a person whose position in life precludes any effective action or vengeance ("...I have to walk away feeling mad"). Obviously Flans loves this mini-trope... it's the high note in the song & its finale. --Nehushtan (talk) 13:09, 23 November 2019 (EST)