It gets people mixing cocktail ingredient right into tumbler (10)
I believe the answer is:
icebreaker
'it gets people mixing' is the definition.
(an icebreaker encourages people to mix socially)
'cocktail ingredient right into tumbler' is the wordplay.
'cocktail ingredient' becomes 'ice'.
'right' becomes 'R' (common abbreviation).
'into' is an insertion indicator.
'tumbler' becomes 'beaker' (both can mean a glass or cup).
'r' inserted into 'beaker' is 'breaker'.
'ice'+'breaker'='ICEBREAKER'
(Other definitions for icebreaker that I've seen before include "which opens dialogue?" , "Something to relax social tension" , "Something relieving initial tension" , "Something helping to start a conversation" , "Reinforced vessel" .)