Pulse output only from switch toggle on OR switch toggle off (not both please)
The trigger input only causes a pulse on the falling edge of A1 as per the functional table (from the datasheet). 



You cannot generate a clean clock edge directly with a mechanical switch, you will get a number of high and low pulses (in general) on opening and on closing, so you definitely need debouncing if you want to reliably trigger the one-shot with a mechanical switch. 

In general, if an edge matters, you will most likely need debouncing. If a level matters you may not need debouncing. 

One method is to use a SPDT switch with a NAND gate like 74LS00, another is to use an RC filter with a Schmitt trigger gate such as a 74HC14 to get a clean pulse (the '122 does not have Schmitt trigger inputs so it would have to be added externally). 







simulate this circuit &ndash; Schematic created using CircuitLab