AdiIRC

Added in 1.5

/ignore [-cdhiklnprtuNwxyCEI] <on | off | nick | address> [type] [channel(s)] [network]

Ignore certain types of messages or all messages from a user.

/ignore with no parameters will show current ignore status.

If you do not specify a type then only the users nickname is used. If you specify a type then the users address is looked up via the server.
The nick will not be hidden in the Nicklist, and join/part/quit/mode messages will not be ignored.
If you have a query window open with the nick, the query messages will not be ignored until you close the query window.
If the ignore doesn't seem to work, make sure ignored is enabled by typing /ignore on.

Switches

-c - Ignore channel messages.
-d - Ignore DCC requests.
-h - Ignore highlights.
-i - Ignore channel invites.
-k - Ignore control codes.
-l - List all ignores on current network.
-n - Ignores notice messages.
-p - Ignore private/query messages.
-r - Remove ignore.
-t - Ignore CTCP requests.
-uN - Remove the ignore after N seconds.
-w - Apply the ignore to any network.
-x - Indicates address should be excluded.
-y - Ignore Tips.
-C - Indicates [channel(s)] is defined. (AdiIRC only)
-E - Ignore emoticons. (AdiIRC only)
-I - Ignore inline images. (AdiIRC only)

Parameters

<on | off | nick | address> - Turns on/off the ignore feature, or if a nick/address is specified, applies the ignore to that user.
[type] - Ignore by hostmask, see $mask for available types.
[channel(s)] - Used with -C, applies the ignore on matched channels, use comma as separator for multiple channels. (AdiIRC only)
[network] - If specified, applies the ignore on that network, otherwise applies the ignore on the current network.

Example

; Ignore all types of messages from 'Nick!*@*'.
/ignore Nick

; Ignore only channel messages from 'Nick!*@*'.
/ignore -c Nick

; Remove 'Nick!*@*' from the ignorelist.
/ignore -r Nick

; Ignore DCC requests from everyone.
/ignore -d *!*@*