horn in

verb

1. To force or come in as an improper or unwanted element: cut in, intrude, obtrude. See enter/exit.
2. To intervene officiously or indiscreetly in the affairs of others: butt in, interfere, interlope, meddle. See participate/abstain.

Intrude, join without being invited. For example, She has a rude way of horning in on our conversations. This expression alludes to an ox or bull pushing in with its horns. [c. 1900]

The verb has one meaning:

Meaning #1: poke one's nose into
  Synonyms: poke into, intrude into, meddle with