Swingy Dingy means when you are swinging your dick, to dry it and other stuff.
Guy: Look guys, im drying my dick!
Another guy: You're doing a swingy dingy!
Swingy-dingy is when you lay on your bed and lift yourself up and smash yourself down, trying to do a wave.
Iām going to swingy-dingy my bed tonight. :* ( if u know what i meanš)